K.F.
Wow tough situation. I'm currently in a different but similar situation. Unfortunately my situation requires I have to evict family from my rental property. Due to circumstances I have tried to be very loving and kind and work out an arrangement which would be beneficial for the entire party if everyone cooperated. Yet I didn't ever have full cooperation. So here we are. In less than a week my family will have to move out and make their own way in the world.
In your situation here are some key things I believe you will need to make this work. Have a few different plans you can present to them. One being the fixing or getting their home liveable, second the possibility of them selling their home as is, and/or them moving back into their home. Of course there are a host of other arrangements that you can think of on your own.
Keep it positive. Thank them for the help they have provided while also letting them know respectfully what you expect from them should they continue to live with you. Let them know you will support what ever decision they make but if their plan is to continue to live with you and your husband there is going to need to be some changes. If they can't abide by these changes then something different will need to happen because in your house you need to have it run a certain way.
My guess is that while it would be wonderful for your in-laws to continue to live with you it just may not be possible. It is very difficult for people to change and it is difficult for grown ups growner than you to humble themselves enough to follow your rules in your house.
Again let them know how much you love and appreciate them by giving specific examples.
Have dates and deadlines laid out. No decision needs to be made tonight but give them a week to think of the options. Have another meeting in a week to discuss the decision they have made. Over the next week see if there have been any changes in the way they treat the kids and you and your husband and this will give you cue as to how to proceed forward.
Long story short, if they stay in your house their has to be a standard and their home needs to be dealt with even if it is fixed enough for someone else to perhaps rent it out but it really needs to go.
Have a list of the topics you want to discuss. Stick to the list, Keep it positive and make the best of it. I praying success for you all.