From what you've stated these are my thoughts:
1) It seems there is an established open door policy. If that's not working, your family needs to change that.
2) Week long visits (and guests) are also the norm. Again, if that's not working, your family needs to change that.
3) The words FIL used might not be how you would phrase it, but maybe his perception is that he is checking with you on dates.
Things you can do:
1) Let them know what plans you have or when it would be a good time to visit. Offer the week before or after.
2) Establish guidelines for guests.
3) Make plans and try to include guests. If transportation is an issue, alternate arrangements can be made.
Remember that grandparents sadly won't be around forever and get to enjoy your children. Interested grandparents are a gift, and as family struggles and personalities can clash, we set our differences aside, so our children will enjoy their company and have lasting memories.
If respecting your parenting choices is an issue, then you or DH need to address that.
I'd also keep in mind a 14 hour trip to see the grandkids is a long trip, mostly likely costly, and being away from home (without friends his age, so maybe that's why he brings someone), but he truly loves and wants to see the little ones.
Organizing activities that children & grandparents can enjoy is a great way to pass time, make memories and free up some time for yourself. Think art projects, a trip to the museum, a day at the park, a picnic, baking cookies, games, etc.