I have a boundary that people who aren’t nice to me don’t get to stay in my home. My home is a safe place for my children, DH and myself. The only people we host are those who treat all of us well. We also have busy lives and only host when it is convenient for us. I couldn’t imagine having difficult people who didn’t treat my children or myself well in my safe space for a few days a year, let alone a few days a month. I would have told my DH it was either me and the children or them after the second month.
I also don’t consider visiting relatives a holiday. I have very little vacation time and refuse to use much of it doing something that I don’t find fun and relaxing.
Growing up, all of my vacations with my mother involved either going to relatives or hosting relatives in our home. I don’t have fond memories of doing fun activities, seeing interesting things, relaxing and bonding as a family. My memories involve having to give up my room to whoever was visiting or having to sleep on someone’s living room floor. Being expected to entertain, wait on and pick up after people that spent their time complaining, criticizing and gossiping. I refuse to do that to my children and myself.
I think it’s time you set some boundaries with your husband. I would first cut out the monthly visits. They can’t manage to be pleasant guests and your husband refuses to protect you and the children from them, so they no longer stay in your home. If they want to travel to your town, they can stay at a hotel or AirBnB and your husband can spend time with them there. If you and the children feel like seeing them, you can go to their lodging and then you can leave when they start their rudeness.
The only way I would agree to travel to them would be if I stayed in an AirBnB and had my own car. This way your husband can visit with them as much as he likes and you and the children can do your own thing when they become unbearable.
Your husband has a long history of good times with them that outweigh their bad behavior for him. He loves them partly because of the good memories and he is used to their rudeness and can easily ignore it. You and your children don’t have that history to fall back on. It seems like most of your history with them involves them being critical, rude and unpleasant. Your husband needs to understand and accept that the behavior of his parents and his unwillingness to stand up for you and your children has created a situation where you and the children aren’t happy around his parents. It is time for him to man up and be a husband and father, not just a dutiful son.