I see that you are having trouble after working on trauma in therapy ...more than before working on it.
Can i suggest a reason?

I used to think i should contain all that my alters had been through...That i should serve them....that i should take memories as MY OWN. and some parts were serving and rescuing others. like you mentioned your T suggests. You seem to have a lot of pain in you because now you - less that 100% you - is trying to deal with the pain that belonged to them.

I have tried something entirely different:
I think there need to be a balance achieved through the entire system.
That every part learns to contain its feelings and take responsibility to actions.

Older parts rescuing younger parts might not be helping because emotions are been thrown violently from part to part instead of being dealt with. Maybe the younger need to be told to remember that somehow they survived, that they dealt with this already. That it may SEEM as thought they were helpless but in fact they are not. Even without adult parts.That they were and are capable of staying alive and independent through all of this.

When the balance is achieved and each alter CONTAIN emotions - and not just messing up with them like our younger usually do - then older can be told to support them. But this happens through communication. Not through someone else taking it FROM them. The parts who was through it needs to deal with it first and acknowledge.

After that you can share the memories all together as an awareness that they all happened to your body. They are real parts of you and without them dealing better independently there will always be this trauma throwing...one can`t deal - the other takes its place. Like a ball game.