I would find it aggravating to have to regularly counter any indoctrination BS my kids were exposed to, or to have to constantly assure them that the way we live is perfectly fine despite the critical, fear mongering crap from granny and grandpa. Raising kids is hard enough, why should I have to do that? Because grandparents. Wow, I didn't know I was some sort of 2nd class nobody that, as an adult, I still had to kowtow to my parents and allow them to disrupt my life and f*** up my kids. Sorry, I didn't get that memo.
Young kids can get confused easily which can be upsetting to them. And sometimes it won't be evident that they're upset or confused. It'll show up as some health or behavioral issue later and you'll be left wondering what's going on, having to pick up the pieces. They need structure and an even keel in life.
My daughter started wetting her bed when she was about 5. We found out soon after that it was because my mother, despite being told to bugger off with the JW propaganda, had told my daughter some typical JW doom and gloom story about everyone being destroyed by god because of whatever. It freaked my little baby girl out. I literally could have punched my mother out for that. I was so mad that my husband had to give my mother the talking-to because I could not trust myself. My husband said he could barely contain himself either. We banned her for 6 months for that. She didn't pull that again.
That is why I'm not at all sympathetic to rolling over for JW rellies. It's not like most other religions. It's far more severe and harsh, which can be frightening to some kids as they're either too young to process that crazy information or just don't have that capability like others might. And the JWs will be sneaky about it too, undermining your trust and your authority because they do not respect you, smugly believing they're right and superior to you. Why should you respect that?
I wish you luck and I hope the relationships with your relatives is worth it and ends up being fine. But just keep a real good eye and ear out, trust no one but your instincts.