Sorry, I think this is unusual at 26-28 with a partner of 2 years, yes.
I would make it clear to him that you're taking it as a clear sign that he sees your relationship as fairly casual... so you will be doing the same.
I think this is the point in life where you are still young... but if you waste years on a man from here on in, you are likely to really regret it.
Take this as a chance to evaluate your entire relationship, very dispassionately. Is everything else really genuinely good? If you have doubts, then be brave. Tell him this isn't the pace you want, this isn't the situation you want, and move on.
The ignoring your suggestion that you join them is a red flag, by the way. At this point, in a good relationship, you'd at least be talking about this, and him saying - I'd like to spend time with you too but THIS is the family situ, I wouldn't feel able to invite you because x y z, I can/can't see it changing in the near future, how do you feel about that?
Not simply being evasive about something you're clearly unhappy about.