OP,
This is your chance to be firm.
How dare they mute you.
Decide what you are prepared to do and tell them to figure it out as they have done.
If you give in now and go back, you have no one to blame but yourself.
You have allowed this to happen and continue on for 7 years which is ridiculous, with 6 siblings.
Take emotions out of it.
Take how you feel about your mother out of it.
Tell them you will be doing a share and no more as you have your son and your health.
They clearly don't care for you or their mother.
So you have to stand up for yourself, your son, your health.
Just do not return to this.
You can also say I am unwell so you will all need to continue to share the load.
Don't step in an become the organiser because they will bail at times and expect you to step in.
Simply say, I can do X and the rest of you will have to sort out the rest.
Drag on your non involvement for a few more weeks so they have more timebto form a routine without you.
I repeat, if you go back to doing it all, you have no one to blame but yourself