I would feel very angry as weddings are not the place to propose. I would not talk to them and if they invited me to their wedding I would say that because of the fact they proposed at my wedding, I will not go to theirs.
I would think that it was bizarre as they could've chosen a more appropriate time but I also probably wouldn't care that much as I don't get angry/annoyed easily and marriage&weddings are not that deep for me
I would feel very angry as weddings are not the place to propose. I would not talk to them and if they invited me to their wedding I would say that because of the fact they proposed at my wedding, I will not go to theirs.
if they told me about it in advance and the couple are good friends of mine I honestly wouldn't care... if they do without warning anyone that's just weird and trying to steal someone's thunder