Tip: I Played as a Sentinel with Warp Ammo (dont know if warp ammo is the best choice... :) here but it seemed to help!)
Max out these abilities
Shield ability and go for -> Raider
Warp -> Heavy warp
Warp Ammo -> Squad Warp Ammo
Rest in Overload
Team mates i used constantly were:
Miranda: Max warp and overload
Mordin: Max Incinerate and Neural Shock
Freedom's Progress Mission - First Wave of Scions
After many hours trying to do this i finally found the only option is to run around in circles around all the crates in the middle trying to avoid the scions as best as possible, whilst simply doing spray and prey on the husks while constantly refilling my sheild using the Y button. Once all husks are gone simply hide in a corner and warp the hell out of the scions from a distance - if you dont target them when u aim at them that is the "safe zone" where they tend not to attack you and u can aim warp etc at them and still make it hit.
Freedom's Progress Mission - Prothean
Try to trap in the middle in between boxes/crates - it glitched and couldnt hit me or my team mates while i sat back and warped it. Keep re-trying until it seems to stop moving OR simply go into cover by a large square or rectangular object and move around it slowly in cover whilst it "attempts" to hit u and let your team mates finish it off
Collector Ship Platforms - See above!
Collector Ship - Prothean
I put my team mates by the cover looking across the gap - hid at the top overlooking them, and waited for the prothean to approach me and did a circular swoop of the area:
1. Hide up top - kill the 2 husks and concentrate on boss, make you team mates concentrate on the boss too.
2. Go right to the right hand side ramp and into cover when it is going up the ramp the other side.
3. Once it is in your spot in 1. sprint and put on sheild and run to the tall square structure on the far left in front of the the cover and hide behind that.
4. Once it begins to come to you again from the other side - run up the ramp to the original hiding spot - dont attempt to hit it too much from here as it usually is too late by then.
This took me several goes and yes it may or may not be the best tactic but it worked for me.
Reaper IFF - Scions
Just hide your team mates miles back from the action (yet husks do respawn - but i did this and managed to let the scions get to a spot where the husks didnt respawn and just took them down from across the way with warp and incinerate and used the "sweet spot" where your not targetting them but can still aim warp etc at them.
Reaper IFF - Boss
Run in circular motion whilst spraying and preying - ignore your teammates they suck and usually die instantly - but revive them as much as poss to distract attention from you. Once the thing opens using a heavy weapon on it until you begin to get swarmed or before - then run around again. This bit was pure luck from me i think.
Miranda - Loyalty mission boss
Head to the left and hide behind the boxes put miranda and mordin into cover and concentrate on the 3--4 in front of u whilst being weary of the vanguard coming up from behind u.
Tali - Treason
The only bit which got me was before you see tali's father's recording at the top of the stairs - the damn geth hunters would swarm you up the top of the stairs. I put miranda / tali into the right hand side looking across the room and not downstairs - i hid by the top of the stairs on the left and just let rip with warp and my geth assault rifle. Again this was pure luck as usually 3 geth hunters come up the stairs - 1 right away and 2 after 3-4 kills of normal geth. On this occasion only 2 come and was able to get the 2nd.