How to make them understand

So in September of last year we had our last natural pregnancy loss. 3 back to back ectopics in 2 years which all resulted in emergency surgery

12/09/2020- ectopic took out my right Fallopian tube

02/07/2022- ectopic pregnancy in the remainder of my right tube

09/12/2022- ectopic pregnancy in my left Fallopian tube.

I’m infertile and our only want to have a biological child is through IVF. We have become at peace with that and plan on starting this April with baselines but we won’t be able to start the whole process until we get approved for a 20,000 loan (we should be fine)

My father in law just doesn’t understand we literally CANNOT get pregnant. Everytime we go over there it’s “when are we having grandchildren?” Usually my fiance stays quite but last time he said “when we get 20,000 dollars for IVF”

His dad proceeds to tell him “nooo you just gotta keep trying maybe fuck in different positions, my cousin had fertility issues and she did IVF then got naturally pregnant with all her kids afterwards so maybe IVF will get things started for you guys!”

His step mom butts in and says “they’re trying so just leave it alone” she understands IVF to an extent because I’ve explained it to her.

We both kinda just looked at each other and my fiancé ended up walking off to calm down (he gets emotional about this as do I but I’m better at hiding it.)

What do I do? Bring a damn diagram and explain to him how the woman reproductive system works? He asks EVERY SINGLE TIME we go over (which isn’t often, just holidays and birthdays)

Advice?