Totally agree with MissA. We have to realise that we are only getting one side of this story and the other side might see it rather differently.
I'm going to sit on the fence and see if there might be another explanation/interpretation for some of the things you mention.
Wanting to be involved in the wedding is perfectly normal, especially if they were contributing to the costs. In my case the soon to be DiLs made sure I was involved in some ways. Shutting them out would, of course, cause problems.
Giant balloon, how big? Some people like to give big balloons for celebrations and many would not see this as a problem (unless they were looking for one).
I would think it would be normal to want to see the baby, why should one grandparent see more of the baby than another? Does a maternal grandmother have more 'rights' than the paternal one?
Mothers of daughters do you accept that your SiL will be closer to his own mum than you?
Of course I don't have the direct experience you have but, reading between the lines, and knowing how often DiLs put barriers between their DH and his family I do think there may be another side to your story.
I think you could go out of your way to improve this situation. Do you really want this to continue? Does it have to be one of you winning and the other losing? Couldn't you be a bit kinder and welcoming?
I am very fortunate to have such loving and generous DiLs who welcome me and want me to have a good relationship with them. I am even lucky enough to be very friendly with one DiL's mother who lives in Europe and comes to stay with us for holidays.