It does seem as if it is not quite so straight forward. Seemed at first older guy, gay couple, racist mum. ....Spoiler alert....
Then it was that as a girl she lost her dad at 13, so maybe was looking for a father figure. I can understand her grandfather being uncomfortable.
The gay guy had been straight, married to a woman and is a dad of two. Of course he can change his mind and be gay, or bi, or whatever - but his parents have obviously found it harder to accept.
And the mum is pretty racist but also finding it hard to accept (or easy not to accept) the fact her daughter's female friend became her boyfriend and now fiance.
What's a bit difficult is the gay guy and the 24 year old seem to expect their loved ones to acceit who they want to marry and be interested in the wedding/or even play a part on it.
And although I can see why they would feel that way, I can understand why their loved ones would struggle.
At the end of the day if your love of the person getting married is strong enough, you may be able to accept their choice.