Since you and your husband had already talked to your FIL and he refused to listen, I think it would be better for you to sort for alternative care. As a mother and parent, I understand how frustrated and fearful and the care taker of my baby refused to take in any of my basic baby care directions. In future I guess your FIL will do more 'annoying' things to your baby and out of control.
There are alternatives such as infant care and nanny which might be more feasible for you. Hope you can sort out the solution soonest.
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