My fiancés family are tearing us apart. How do I play this?

So they’ve always been friendly to my face but over time I’ve noticed a few things and it has made me wary of them.

- When I got a male assistant in work and the dad said to me in front of my fiancé “oh is he single”. He said it in front of my fiancé and I thought it was manipulative.
- They’ve never once paid for a meal. My fiancé has paid EVERY SINGLE TIME and they say nothing. I feel like they are users.
- We got engaged after a year and they weren’t particularly happy for us. We met them to tell them all about how he proposed etc and they did nothing but talk about themselves! I made a joke to his dad about being my dad and he said “oh no not yet”. I felt like saying you can get fucking used to it because I am still marrying him whether you like it or not!

- everything has come to a head over money this week. They already “borrowed” £1500 off him to build an extension and before they paid him a penny back they were buying hot tubs etc! Found out they have defaulted AGAIN on their mortgage and may lose their house and have to go to court AGAIN. Then right before me and my fiancé go on our first ever holiday (because of covid) they get him to go to their house and start crying and putting pressure on him to the point where he doesn’t enjoy the holiday. To say I am angry is an understatement.
-Then when we get back off holiday he says he is thinking of taking out a £14,000 loan for them that they may or may not ever pay off…

I threatened to leave so he has told them he can’t do it and has to put me first but I listened in to the phone conversation and they were Still putting pressure on him.

We are trying to save for a mortgage and wedding and basically our futures.
How should I handle this going forward?
My fiancés family are tearing us apart. How do I play this?
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