Dealing With In-Laws' Dysfunction
Be honest with your children from the start. Explain your concerns about your in-laws' dysfunctional behavior. If having your in-laws and your children in the same setting will do physical or emotional harm, keep them apart. If the situation only warrants contact by phone, then that can be the extent of their contact.
On the other hand, if your concerns are about poor hygiene or bad social habits, explain to your kids that the moral and social values that the children need to live by may be tested when their grandparents are present.
In one case, a young woman with children was continually challenged because her mother-in-law had problems with alcohol at family gatherings. The mother-in-law's adult children instituted a tough-love approach in that their mother could not have cocktails at family parties. If she didn't abide by this request, she had to leave. Let your children know, too, that although your in-laws may have behaviors that you don't like, kids still need to be respectful and kind to their grandparents.
Set boundaries when dealing with your in-laws. Let them know that building a relationship with the grandkids is not only important, but it is also a privilege and a work in progress. It will take time. Show both parties that you are willing to work to make this a successful journey.