You’re clearly nice, decent people who have encountered a pair of selfish, transactional users. Don’t beat yourself up over it, it happens. To them you are just a nice couple they chat to at football (or whatever) and they felt too awkward to say no to you when you asked them over for dinner.
It sounds like you treated them to a lovely evening with amazing food but clearly, they don’t have these skills (me neither) so played it safe with a takeaway when you when back to theirs.
I just think you haven’t read them right and they are subtly keeping you at arms length and keeping their older, closer group of friends as their entertaining circle. They were only ever friendly acquaintances and never intended to be anything more.
They invited you to the paying venue because they needed numbers and as it finished at 8pm (weird) they always intended to invite their close friends back, because who wants to barrel home, drunk, in the early evening when you’ve paid for a babysitter.
Inviting that nice couple from football along to their house party would totally change the vibe, plus if they live in a 3 bed semi they wouldn’t have the room for everyone. I do understand it, but obviously it stings if it’s you on the receiving end.
Just smile and say hi next time you see them, learn from it. People are different that’s all.
Having said that, nothing could convince me to stuff £200 of cash in an envelope and hand it to a man I barely know to pay for his wife’s party.