Give your kids the gift of learning from failure
You and your husband need to take great care of yourselves by setting limits, not only with your grandkids, but with your kid and kid-in-law. Continue to use the same strategies that you have always used as a parent, grandparent, and teacher without any consideration for your kid’s newfangled, nonsensical “we don’t say no” philosophy. Here’s how I would explain it to your kid and kid-in-law when the grandkids are not around:
Kid Whisperer: I know that there has been tension between us in regard to your kids. From now on, I will not tell you how to hold your kids accountable. In turn, I am going to ask that you not tell us how to hold your kids accountable when they are at our house or when they are alone in a room with us. You can have your way of doing things and we will have ours.
More Kid Whisperer: How to stop that fleeing 3-year-old!
Kid: We believe that since our child's chi is in the rising condor, she is more susceptible to negative vibrations coming from your inner phlorb. If you say "no" to her, she could die.
Kid Whisperer: As I was saying, this means that we will not undercut your way of doing things and we would only ask that you not undercut ours. Just to be clear, if you are not in the room, we will hold your kids accountable to the way we do things, but when you are around, you can take the lead. If you don't want us to be involved with discipline, feel free to stay with us while your kids are in the room.
More parenting with the Kid Whisperer: Mom or servant? Hmmm…
Kid-in-Law: We read online that if you say "no" to a child under 10 that they will physically, literally explode.
Kid Whisperer: Alrighty. Also, lately it has been pretty difficult to be around your kids because of their behaviors. We will be able to hang out with you all as long as your kids and your family dynamic are pleasant to be around. We have gained a lot of wisdom about kids from parenting and from teaching for many, many years and through lots of struggle. We aren't really willing to do any more struggling. So, from now on, when the going gets tough, we are going to get going. As in we are going to leave you guys and go about living the lives of happy retirees. We aren't going to try to get you to come around to the way we have learned to parent over our many years of experience, but we also are not willing to suffer through dealing with our grandkids when they are being unpleasant. We won't mention anything more about parenting unless you want to talk about it. We love all of you no matter what.
In this way, you may lessen the amount of time you spend with your grandkids, but you will actually increase the amount of quality time. You will be able to let them know how strict you will be and you will be able to remove yourself instead of having to watch your kid and kid-in-law train your grandkids to become people you don’t want to be around.