You need to pause and think what's going to produce the best outcome here. Don't lose your shit - if you go full court custody mode it will put your ex on the defensive and your family will probably make little effort to include your daughter in anything family related. That might be what you want, but it doesn't sound like that.
Court custody battles are long and expensive and from what I've seen, unless you're able to prove the other parent is abusive or severely negligent they won't give you 100% custody.
If your ex wife has a better relationship with your family than you do and this allows your daughter to be able to spend time with cousins - does it really matter that they didn't consult you? I mean, the child's mom made the arrangements (yes, it's your family...but the situation is really bad).
The person you should talk to is your ex and let her know you want to be aware if your daughter is going to do something with your family and get together and put ground rules for both JW grandparents/family when with your child. No mention of Jah/armageddon/bible/etc or religious topics in general. I have that rule with my JW family.
Bottom line is..do you really want your daughter to have contact with your family and what's the best way to achieve that? In an ideal world, your mom would be someone who is respectful to you(or at least while your daughter is with her). Doesn't look like she's capable of that. Are these people you want your daughter around? These are the things you might want to reflect on first.