Well, that was the game original idea...a party of 15 ppl was supposed to be an easier way to play alliances...its dead now tho.

But i do think your idea do makes sense...you mean a "merge invite", right? So the inviting PT would automatically receive the invited party members if their leader accept the merge invite, right?

Its not a bad idea indeed. Would make things much easier for both sides...but for this would be interesting some kind of "party status" option when you target someone already in party so you could check the other party situation (like number of members, classes and rank)...or else it would still need effort asking number of members, party rank, if they want to join, etc.