Personally, I wouldn't tip each person the same. I would do 20% for each based on how much the service was.
I feel like since they're doing different jobs it shouldn't be too much of a problem; if you were to get two different facials in the same day by two different people with the same title, I would tip the same regardless if one was more than the other! (I'm aware getting two facials in one day is not something that people do but I don't know how to express my idea other than with that example)
Basically what I'm trying to say is since they're completing different jobs, the same tip shouldn't be expected. Of course, since it is near the holidays, tipping them both 20% based on the more expensive service isn't a bad idea (but don't feel expected to do so)!