Sadly conditioning in JW land goes deep and unless someone has truly broken free from its control then they are able to continue to push buttons. You were right to identify that there is no compromise in this religion and they will expect you to accomodate them not the other way around. Coupled with this recent articles and assembly programmes have whiped JWs up into a frenzy about unbelieving relatives it is a powerful mix.
If visits are unpleasant and unannounced I would put it to your husband that unexpected visits are not a good idea since he has obviously gone to some effort to come and cannot expect it will always be convenient. If your father in law arrives unannounced then state you are sorry but you and the girls have other plans and you are on the way out. Be friendly and regretful but get out of there.Your husband does not want to confront his parents but the longer he leaves it then the worse it will become. If he does not believe then he needs to make sure they know that, then his parents will either shun him completely or he has the basis to say to them that their religion is not a topic he wants to discuss. He does not need to be unpleasant but he can disagree without being disagreeable.
I would also have a family meeting and you and the girls express your concerns about his mum and dad and how they make you feel. Tell him your fears and how you love him but feel that he is being pulled in all directions and it can't be comfortable for him. Ask him how you can help him to stand up to his parents. At the very least ask him to request no further visits from elders since they serve no purpose, he is not intending to go back so why waste their time. If he cannot stand up for himself then ask him to at least make a stand for his children and set ground rules with his parents about them. For example if they are unhappy with their behaviour then they address it with you or your husband and do not shout at them. He must surely want your children to have a good relationship with them but at the moment they do not and that is sad for all of you.
If he is still allowing them to control him then it will be a slow process he needs to stop thinking about himself and start thinking as a husband and father and that takes training and time.