Thank you for all your kindness and thoughtful comments, I'm sorry I haven't replied to you all individually.
A few specific points have been mentioned that I will explain:
Yes I do think BIL2 has mental health issues though I don't really know him well, he does show some very strange behaviour traits.
FIL is their stepdad, their father died when the brothers were aged 5 to 15. FIL and MIL met and married after the brothers were grown up and mostly had families of their own.
Although FIL is irritating we will do everything we can to make sure he is protected, unfortunately he is his own worst enemy at times.