Great write up on how you lead in supporting survivors of financial abuse or coercive economics (keeping it short)
If I recall correctly, when setting up a joint account, both parties had to separately approve.
Maybe a similar check can be made and requires both parties agreement for large withdrawals or those that go above the amount added to the account needs the other person to approve.
You could at a setup step around funding splits between the joint holders… That would be like a baseline and support reviewing changes over time… Appreciate this would depend on the type of account and Intended use…
I don’t suggest this solves anything, but merely adds another layer od possible protection.