But you seem to be suggesting that this group of 5 (or 6, or 10, or however many it is - OP won't say) are only allowed to do things as one homogenous group. That's weird.
Even if it were "only" 5 or 6, it is really difficult to get people together to do X or Y when it is that number. As an example, I try to meet up with other retired colleagues about once every 2 or 3 months for lunch. We (by default) are all retired so you'd think that shouldn't be too difficult, but it is rare all 6 of us can make it on the same day. That's just lunch, not a weekend away. Another example my brother was telling me that his family had been given one of these City Tour game / puzzles / experiences last Christmas, and they have just not been able to get all 5 of them together to do it once during the last 11 months.
I enjoy my group's friendship, and enjoy meeting up with them, but I would be amazed if any of us thought that all 6 of us had to be invited if 2 people were going to something together. That's just bizarre, the idea that people can't see one another in 2s and 3s. Really odd.
I can't think of anyone I know, from any of my groups of friends who would expect a whole gaggle of people to go to everything together. You'd end up never going anywhere if someone actually tried to impose that rule.
Are you genuinely saying that when one of my friends messaged me a couple of months ago to ask if I'd go to a concert with her that evening because her dh wasn't feeling well and they didn't want to waste the tickets, that I should have replied that I couldn't go as another friend might have their feeling hurt because there wasn't a ticket for her too ???
Or when I was going to an attraction I thought my friend would enjoy and had a space in my car, I shouldn't invite one friend because another might 'feel hurt' if I didn't invite them (which I couldn't because there was only room for one) ?? 