Two Hmua??

I think you should only look with an HMUA that can work with all types of hair and skin types. I will say I have found the ones of color can adapt to all skin types but not all do. I would not look for one rather a studio that has many as they can work together. The owner of mine is Indian but she has HMUA from all over so they can do all brides. It was important that I had someone that could deal with extensions and my skin tone.

I would look for a hair and makeup artist that has worked with all types of hair and skin types because most hmua have a exclusivity clause like you mentioned. The other option would be if you go to different salons. For my brother's wedding, his wife forgot about hair and makeup until weeks before the wedding. My mom, sister and I had to go to one salon and her and her mom went to another. None of the salons in town could accommodate all of us.

You should be able to find a person who can do all of the above. I've seen some women, normally minorities, who are able to get tgeir hair done the night before the wedding and maintain the style perfectly the next day.

Browse Thumbtack.com and look through their portfolios. Get a trial first and then decide who to go with.

As someone with curly hair, make sure they can handle the curls! If they can do that, they’ll be fine with straight hair. That’s what most do the majority of the time.

Definitely look for a stylist that can work with everyone's hair type and skin tone! Some vendors won't work with other vendors on the same projects, or will but think it's rude. Anything to keep the drama down to a minimum. Plus having one person, or two people that work together do it will ensure the vision and look is more cohesive. Too many HMUA could clash with the overall look and vision.

I would look for someone who's comfortable working with your hair and skin first. 1. You're the bride so you're the most important, and 2. I guess this could depend on where you live, but if you live somewhere that most people are white, most hair and makeup artists will be comfortable working with straight hair, but you'll have to look harder to find someone who knows what to do with your hair.
(Sorry if that was worded really awkwardly. I actually have thought about this a lot. Hopefully you'll understand what I meant anyway.)

You should definitely hire a HMUA that you feel comfortable with and that you feel understands your complexion and hair texture and type. I think a talented HMUA can understand and work with a gamut of skin tones and hair textures, and I feel that it will be possible to find someone who can do all of the ladies you mentioned. In general, I think very dark and very fair skin tones are the most difficult to color match, and curly/natural/textured hair is more challenging to master than straight hair, so I'd find an HMUA with a knack for your coloration and hair type and then they should probably be able to handle your mom and bridesmaid.

Depending on where you live, you might find that HMUAs have a lot of experience working on diverse clients, or not. I live in New Hampshire and work in Vermont where the population is overwhelmingly white. I work at a college and students of color on campus used to drive an hour to a barber shop in Massachusetts that knew how to work with natural textured hair, so now we actually have a barber come to campus 1-2x a semester so that his talents are more accessible to our students that need them. The barber cuts all hair types, so his services are not just limited to certain students, but it really fills an important void in our local community for our students of color. My husband has tightly curled hair too, and his hair cuts are wildly irregular if he doesn't consistently go to the same barber each time, whereas my fine, wavy hair looks pretty much the same regardless of who cuts it.

I would default to finding a stylist whose skills due justice to your beautiful curly hair and darker skin, and I'm sure they can probably pull off a great look for your lighter companions as well. I would ask to see a portfolio of their work representing diverse clients to ensure that both the dark skinned, curly haired beauties and fair skinned, straight haired beauties look equally gorgeous.