I met DH at 21 and I moved into his flat at 23. We were both not particularly interested in being married but eventually eloped when we were 35. During that time we were living together I was financially vulnerable as I was paying the mortgage on the property and my name wasn't on the deeds and I hadn't done anything legal to protect myself. We were also both financially vulnerable if something happened to either of us as we hadn't written wills.
It all worked out ok for us still together after 28 years, but in hindsight getting married earlier would have been a better decision for both of us legally, even if it did end in divorce.
The concept of modern marriage is now flexible and different for everyone, you can say the vows you choose, which is a good thing. I do believe if you shouldn't make a commitment to be with someone unless you mean it, whether it is buying a home together or marriage you should endeavour to ride out the rough (obviously excluding any kind of abusive relationships) with the smooth and do your best to make it work, but if you try your best and it just isn't working out there is no shame in marrying young or more than once.
So if I was invited to either of OP's weddings I would think a wedding, I love weddings! and what can I wear!
If they have made vows before and broke them by divorce then a second marriage is a little regardless of age. It makes a mockery of the vows.
Yellow, if the vows say to love, honour and cherish and your dh stops loving, honouring and cherishing you and is basically a moody nasty arse and there is no chance of him changing are you really going to stay until death us do part and make both of you miserable for the rest of your lives? You only get one life and in the modern world divorce and remarriage is no longer judged on the misplaced values of the 1950s.