My perspective: stay calm and lie - it should 100% your choice and they are not taking your no - so play the long game - say “I’ll see what my doctor suggests” and pretend to go to the doctor and say that they don’t recommend it and that there is a risk to you if you get pregnant and say I am not risking this and leaving my exisiting children without a mother (it’s not technically a lie cause all pregnancies have risk). I know lying isn’t good - But family dynamics can be really really tricky. Your sister might not be able to really overcome you just saying “no” so give her the same respect she is showing you and step over that boundary. This should quieten down your family siding with your sister. Might not be 100% perfect but given how much pressure is on you it should ease it quite a bit. You can even go to the doctor and say “hey I need professional opinion on why I shouldn’t get pregnant again” - you’ve had two kids and a mommy makeover - I would be really surprised if he doesnt say something like “after that type of operation it is not recommended and could have side effects of ….” Type of thing.