I am sure your ex-SIL has thought of the ramifications of inviting you and I doubt his bride to be would have agreed unless she thought her parents would be happy. Personally, I feel that it is an honour to be invited and I can't see why you think you know better than them about the appropriateness of their guest list. If there are children involved I think it is a good way of role modelling decent behaviour in a divorce unless you think that the invite is a two fingers up to your daughter.
The Republic of Ireland and their tensions with migrants.
My four year old grandson "doesn't want me"