It doesn't sound like you want to leave your job, and I am doubtful you or they want to live on a foster carers salary - I think you'd be nuts, basically.
I'd take a giant step back, and -
Raise merry hell with your employer re adoption leave. What multinational corporation wants the bad publicity of refusing adoption/compassionate leave to an employee kind enough to take on three kids?! None I would say - you are just talking to people too low on the food chain. Get advice from an HR consultant / your union (pay for it if you have to) and negotiate some leave and some staggered return to work.
Raise merry hell with SS, again, get yourself to the top of the food chain - you have a job that you need in order to support these kids and so meetings have to be arranged on X days and that is it. In exceptional circs, you will try and arrange a zoom on another day. Do you they want to find another placement for these kids? No they do not. This one might be tougher to achieve than your work, because of so many agencies being involved but I bet you can improve it 80% given time and toughness.
Do you have good childcare and enough help with outsourcing household tasks, get that in place if not.
You may eventually want to look for a more flexi career, but you want to do that while you are still employed, and ideally after the initial shitstorm has calmed down.