[quote=Beta]
Sounds to me like someone didn't do all the loyalty missions or upgrade their team properly.Or simply picked all the wrong people to do each leg of the base.Garrus or Miranda for leader roles.Tali or Legion for Hacker.Jack or Samara for Biotic.Mordin for Crew Escort.
[/quote]

No way man, I've been upgrading everything and I did all the loyalty missions and I picked the right people for the different parts of the mission. They all survive just fine up until I leave to kill the reaper. Maybe it's because I play Renegade?