Bridal party hamu

I think your BMs will understand since she is your sister and MOH!

I would maybe ask any of your bridal party if they would like to get theirs done. If you are not requiring it, you are not required to pay. I probably would go that route just to avoid hurt feelings.

I think you're asking if it's okay to only pay for your sister's HMA? Short answer: yes. Longer answer: she's your sister and I feel that makes a difference. However, as Hannah said, maybe offer to your party. Check with your artist, bridesmaid hair and makeup is usually cheaper than bridal. After you know prices you could say something like "the HMAU doing my makeup is X cost for makeup and X for hair, if anyone is interested in having it done professionally. Let me know so she can schedule time for it and I will need the money by X date. Please know you aren't required to use her or get my professionally done and can do it yourself."
Also, with this done (or even without it) no one needs to know you paid for your sister's. For all they may know she could've paid for it- especially if you give them the same opportunity.

If you are asking about paying for their hair and makeup, it is absolutely not required for you to pay unless you are making them get it done. I would let them know that hair and makeup will be available and let them know the prices and ask if they would be interested so you can check with the artists to make sure you have enough time.

Ehhhh there’s a way to do this right and a way to do this wrong. I think it’s okay if you only PAY for your sister/moh’s hamu but I’d do so privately and as a gift. I would say you MUST offer the professional services to everyone, but also indicate that they would have to pay their own way (and then tell your sis you plan to cover hers). What is not okay is to simply book your sisters and not offer any pro services to the other girls and have them show up the day of sitting there awkwardly doing their own while you all get pampered— so I think you need to include them with an invite to partake in the services, but it’s fine if you don’t pay for them all.

I'd give the other girls the option to if they want to pay for it.