Ring Bearer and Flower Girl

My fiance's niece and nephew are going to be in our wedding so my fiance and I talked with their mom today about their attire. She thinks the nephew should just wear khakis and a button down shirt from Walmart. However, my fiance and I would prefer that he wear a tux to match the groomsmen and my fiance. The tuxes are black so khakis and a button down wouldn't match. I also sent her links to dresses and shoes on Amazon as she mentioned that her daughter would need shoes for the wedding. We were under the impression that the bride and groom get to pick what the ring bearer and flower girl wear, but she doesn't seem happy with any of our suggestions. In fact, she went on a rant about how it is completely unnecessary that for the nephew to wear a tux as he is only three years old. She said that we are being ridiculous for even thinking that is a good idea. Also, during the conversation, she also asked if I planned on hiring a professional to do hair and makeup for the bridal party to which I said yes. She said her daughter will definitely need to have her hair and makeup done by a professional. The niece has been in beauty pageants for years so I guess it really shouldn't surprise us that the mom thinks her hair and makeup need to be professionally done. However, I don't think it is necessary for a six year old to have her hair and makeup professionally done. I am also not sure if she is expecting us to cover the cost because we don't plan on paying for anyone else's hair and makeup as it will be optional. My fiance and I have no problem covering the cost of the tux for his nephew as it is only $80 or the cost of the dress and shoes for his niece, but I do have a problem covering the cost for hair and makeup. If they didn't live seven hours from us, I would offer to take them myself after this pandemic is over to get their outfits, but that's not an option. Are we being selfish for wanting them to wear certain clothing for our wedding or should we let her decide what they wear even if it won't match the attire of the groomsmen and my fiance or the formality of our wedding?