**There is no difference. ** People have become used to divorce and remarriage in our culture and try to make it somehow “ok” or just ignore the obvious. God’s law on marriage is natural law and it applies to ALL people, everywhere.
That said, we have no way to know with certainty if prior non-Catholic marriages were valid or invalid. And, of course with the non-baptized a natural marriage is dissoluble under certain circumstances such as the non-Christian converting to Christianity and marrying a believer.
Therefore, in general, with non-Catholics we tend to give them the benefit of the doubt since we really cannot know with certainty the validity/invalidity of their attempt at marriage.
So, yes, if a non-Catholic is “remarrying” after a divorce on the surface it would appear an invalid marriage. But, if their first spouse had been married before, then they had a ligamen impediment and really were not validly married. Therefore, this marriage would be valid. That is only an example of how tangled non-Catholic marriage attempts have become due to their continued drifting from the biblical principles of the essential properties of marriage and the prohibition of divorce.
If you, knowing the facts of their specific circumstances, believe that they are entering an invalid marriage then you should not attend. If you believe it would send a wrong message regarding condoning divorce/remarriage, you should not attend. If you have reason to believe that their prior attempt(s) at marriage would be viewed by the Catholic Church as invalid (or if they are unbaptized and could possibly have a Pauline Privilege situation going on) then perhaps you can attend.
As I have said in several previous threads you have started-- it is a prudential judgment on your part.
It is even a prudential judgment to attend when you know it is an invalid marriage-- for example, two Catholics marrying outside the Church. We would typically not support this or attend. But, pastoral guidance can be given if for example the parents of these two people believe it would cause irreparable harm to the family relationship. If there is hope that by attending the parents can continue to work towards getting their children back in to the Church then it *can *be permissible to attend if they are clear that they are not condoning the marriage outside the Church, object to it, etc.
Kinda like the fact that a non-contracepting spouse can have marital relations with the contracepting spouse to preserve the conjugal union if they make their objection known and continue to try to move the marriage to a state without contraception.