On my first playthrough of the game the only person that died was the tech specialist because I had Miranda lead the second squad and she wasn't loyal (strange that me tell her that Jack was a valid crew member means she lets Tali get killed in a mission, but whatever).  I'm doing a renegade play through now and I want for everyone but Morinth and Tali to die, but everyone except for Thane is loyal to me. 
 
Is it possible for people to die by assigning them to terrible positions, like making Zaheed or Jack a team leader and putting something with horribly biotic abilities as the biotic specialist or is it all based on loyalty?

Yes it is. I had everyone loyal and when I changed the assignments some of them ended up dying.
 
Zaeed leading Team 1 seems to leave the Tech Specialist dead (Garrus seems to have worked)
Using Samara for the bubble Garrus died leading the Second Team. (Jack worked for the bubble w/ Zaeed or Garrus leading Team 2)

When you have unloyal people in your crew, or assign jobs to unqualified teammates, someone will die.  If you assign Jack as a squad leader, she might die, but there is also the possibility that another crew member will die because Jack does a bad job.

It's a combination of everything, really. Jack might have strong biotic powers, but if you don't give her the L5 Implants, there is a possibility that if you assign her to a biotic-strong position with loyalty, she may die. If Thane is loyal, but you have him assigned to Fire Team, he could possibly die.
 
Why would you want people to die? Zaeed was a dick, but he redeemed himself after he gave his life to make sure the Normandy crew got to safety.

Yes. Tali died due to Miranda not being loyal for me.

Loyal squad members can certainly die when you make wrong decisions during that final sequence.
 
For example, a loyal Mordin has a pretty high chance of dying at the door when told to "hold the line." A lot of people complain that this is a glitch, but think about it. Is a scientist really qualified to stay bunkered down and hold a position against an onslaught? No. Even though he was STG, his missions there were covert and he was more of an infiltrator than a straight up soldier. I always send him back with the crew, or have him with me for the final battle.
 
Another quick example, a lot of people complain when loyal Grunt dies leading either of the fire teams, or causes someone else to die because he does a poor job. He sounds qualified, but would you really give an adolescent Krogan a command position? I think not.
 
All in all, I nerded out and roleplayed my decisions during that final battle and no one died. Haha.

Mordin's brutality is amazing. He'll find cures for diseases and be humane about it, but if he needs, he will execute somebody in cold blood.

Everyone got through for me. I had everyone loyal Tali did the tech work, Miranda let the fire team, Samara did the biotics with Jacob leading that fire team, noone went back with the crew and I brought Garrus and Miranda with me for the final battle.

Yeah, everyone was loyal for me first time through and both Jacob and Zaeed died on me.

" All in all, I nerded out and roleplayed my decisions during that final battle and no one died. Haha. "

I've read some posts about people saying that basically everyone in their squad died except like 2 or three others.  I went out my way to kill everyone and only got 3 deaths.  Everyone except for Thane was loyal and I think that was what kept them all alive.  The choices I made are: 

• Tech Specialist: Garrus, seemed like the weakest Tech guy from the options.  KIA 
• Squad Leader: Thane
• Biotic Specialist: Jacob, seemed like the weakest Bio guy from the options
• Squad Leader: Thane KIA
• Teammates: Jack (KIA) and Miranda 
• Nobody helped Dr. Chakwas

"Why would you want people to die?"

In my second game I wanted to see what would happen if I had unloyal crew members, even if I gave people jobs they were good at.  I also wanted to see what would happen if I didn't take Grunt from his tank, and let Cerberus have Legion.
 
Basically nothing.  The two unloyal team members died.  That's it.  Being that it was my secondary game, I really wanted to see the chaos of unloyal team members.... but it amounted to one of them dying while we were escaping and the other dying while leading a fire team she wasn't equipped to do.
 
 
In my initial game, I had no casualties, I did all loyalty missions and side quests... and I save-scummed it at one part, because I figured Mordin had enough experience to lead a fire team.  Close quarters!  Problematic!

" Loyal squad members can certainly die when you make wrong decisions during that final sequence.  For example, a loyal Mordin has a pretty high chance of dying at the door when told to "hold the line." A lot of people complain that this is a glitch, but think about it. Is a scientist really qualified to stay bunkered down and hold a position against an onslaught? No. Even though he was STG, his missions there were covert and he was more of an infiltrator than a straight up soldier. I always send him back with the crew, or have him with me for the final battle.  Another quick example, a lot of people complain when loyal Grunt dies leading either of the fire teams, or causes someone else to die because he does a poor job. He sounds qualified, but would you really give an adolescent Krogan a command position? I think not.  All in all, I nerded out and roleplayed my decisions during that final battle and no one died. Haha. "

"who the F is zaeed? "

dlc for cerberus network thing. the code you get with the game or pay 1 200 ms points for. 

i had legion die as the tech specilist and samara as the second team leader. 

samara for the biotic part while using thane (by mistake) for the second team. he died.

the rest made it.   

After replaying the game from the start and doing the collector ship a few times I finally got it to where only Me, Tali and Morinth survived.  Technically Grunt is still around but he's still frozen.

First go around I lost Legion, Garrus, Mordin, Miranda and Samara.
 
Second time I lost Tali and Samara.
 
What made me do it again (I only got to rent it) was Legion was my favorite people and he died because I didn't have the shielding and he died in the engine room.

In my first playthrough I acquired all (or most) upgrades for the Normandy, so nobody died when the ship attacked. All except Jack were loyal because I sided with Miranda when they both argued. I had everyone on board of the ship (except Zaheed or whatever his name is) and pointed Tali as tech specialist. She made it through the vents and closed the door, no casualties. Then I had Garrus lead the first fireteam and everyone survived. After that, I found the crew and half of them were already dead (took a mission from Liara hoping that I could recruit her and also did Legion's loyalty mission) so I sent Jack and the crew back to the ship and she died, but the crew made it. Thought she would be the least useful ally since her loyalty was normal. For the second fireteam I assigned Thane as team leader and he died defending the gate. Finally, I took Miranda and Grunt for the last fight with the reaper and all remaining party members survived.

So after all I lost Jack, Thane and half the crew. Not so bad but I regret about Thane since he was the only one to welcome my FemShep as more than a friend. Fuck Jack I don't care about her. I'll do a MaleShep playthrough this time and see how everything works out.