Bridal Shower... invite Fh’s aunts who I’ve never met???

I wouldn't invite them unless your fiance is close to them, which it sounds like he is not. If they want to host a shower for you, they can. But it sounds like fiance has his own boundaries set and you should respect those.

Are the aunts invited to the wedding? If not, then easy answer - they should not be invited to the shower. If they are, I still probably would not recommend inviting them to the shower. If I was one of the aunts, I would find it a little odd to be invited to a shower for someone I've never met (usually showers are somewhat intimate affairs), and wonder whether you were just looking for extra gifts. And I wouldn't invite them just so dad's GF will come, either. I've suffered through baby showers where I didn't know anyone. Sure, it's uncomfortable and awkward but I made the best of it because I wanted to be there to support my friend. If she can't find that within herself, that's ok; just accept her decision and let it go.

Assuming MOG is out of the picture - there is a commo tradition of inviting the older women of the family, Grandmothers and Aunts of the groom, specifically to meet the bride, and her family in a shower setting. It is nicest to invite a small group, not an individual. As with a groomsman's girlfriend who does not really know the bride, the expectation is that they give a gift the size of a hostess gift, $10-15 each, or combine to one very small gift, not that they would give a big gift. Though I have been to some such showers when 2 aunts and a great aunt ( grandmother's sis) took a collection in the family, or reached i to their own deep pockets, and gave a $500- $700 gift or 2. Base it on whether you and your groom would like to cut free from much of family, but actively become newly acquainted with these people as what is good in his family. Their grandbabies will become your children's cousins. Such a positive gesture can mean a lot. Sometimes a parent who is a misery to live wit, made their siblings miserable for years. So you and they step aside and become friends on your own merits. If that is what you want, it is not gift grabby. They are not expected to bring more than a box of chocolates, or of nice stationery, likr blank thank you cards. The social gesture is really important to heal a family mess . Make the groom family to the good parts. Many aunts and uncles invest a lot of time and energy in their sister and brother's children, only to have these nephews and nieces torn away . Bring him back, if you can, in a simple gesture like a shower and wedding invitation. It is fine Etiquette.

If they’re invited to the wedding then yes invite them to the shower. If not then don’t invite, the dad’s girlfriend doesn’t get to dictate who’s being invited.

If they are invited to the wedding, I would invite them to the shower, but not necause dad's GF demanded it. It's a nice thing to do to symbolize two families coming together. If they don't come, they dont come, but I don't think they'll find it odd that they are invited