Just Jack and Jill invited.

Usually significant others aren't included unless they too are in the wedding. I would just recommend making sure this rule applies to all significant others.

A mixed group that you yourself are hosting is not a bachelorette or a bachelor party in your honor, it’s a vacation trip. Sorry, but IMO it would be rude and inappropriate to leave out partners in this situation.

SOs are not invited to bachelor/bachelorette parties. You are definitely not “wrong”, nor required to invite her to any of the events. However, you also cannot dictate who people bring on a trip. I would have your fiancé reach out to the groomsman and let him know that no one else is bringing their spouses, and that the events you have planned will be wedding party only. If he still decides to bring the girlfriend, she will be in charge of entertaining herself, separate from him and everyone else (which they may be totally fine with).

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Yep, this. You cannot keep her from coming to whatever place you're having the group vacation in.

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I disagree with this. If you're intention is for this to be your bachelorette/bachelor trip, invite who you want! Leave out who you want! We're also doing a semi-joint trip to Disney and Universal. We're splitting the costs of everything pretty evenly amongst everyone in our groups. But the intent is still this is our party.

Even if this is "a vacation" for you, you're still saying you guys are fronting the bill. Why would you want to pay for someone you don't want on the trip?