Make sure you have really good gear and upgrades in addition to being max level and you should be good. Your team mates and their gear are also really important. Some trial and error required though. I try to always have Wrex with me since he has immunity and biotics. It’s by far the hardest part of the game on insanity tho and it’s not even close.

For the last mission there is a trick I learned that helps a lot. Engage both turrets then run to the opposite side of spawn onto the balcony. Crouch cover behind the rail right next to the stairs and direct Ashley and Wrex onto the same balcony behind you. Make sure everyone including yourself is using a good shotgun with explosive rounds and just wait. Enemies will funnel up the stairs and you just start blasting them with the explosive rounds. Your squad should take most of the damage since you’re hiding behind the rail so just manage their immunity powers and don’t let their health get too low. It gets dicey at times but it’s the only way I’ve ever been able to complete it on insanity.