I don't think what his friends want matter. Really.
This is about their relationship.
Is he willing to consider his girlfriend/fiance/wife's wishes re one trip every couple of years when she is being open-minded about 2 months of hunting he does every year?
If he wanted her there, he could make his friend understand. They already know that his friend's wife will be part of the bucket trips in the future. That he's not considering a modification earlier for his own partner is telling.
He can "make" his friends understand?
The other woman going in the future is not a done deal. We know nothing about it other than what the OP has said. That's a situation for those 2 to work out.
The OP has stated several times this is not the kind of marriage she wants. That is very telling.
Ultimately, what was said about not following someone else's advice is the key. Seems in sharing her thoughts she's finding her own solution.
To me, this isn't the type of situation that young people considering marrying come across. Meaning the switch from hanging out with guys to pairing off, leaving one or two guys who just don't get that no one wants to hang out at the sports bar anymore.
This appears to be the time tested relationships of mature men who have complex, rich bonds that go beyond the activity of hunting.
Me, I would have to question my need or motive for wanting to change this time honored, dare I say sacred tradition that involves not just 2 people, but an entire group.
This his his bucket list, not theirs. They can write another bucket list of their own.