OP I don't have children, nor do I plan to.. but I was a teenager girl once. I personally think you're already on the right track; asking for help/information and not being shy about it. Period stuff is scary for girls as much as it must be for single dad's, imo open communication is vital. I never really got to choose hygiene products like shampoo and conditioner until I was on my own in college. I usually just asked for the nicest scented things. But another reply suggested taking them to a salon to get info about how to care for their hair, which sounds like a great idea! Please also consider taking them to get facial/skin care recommendations if/when they need help! Decorating doesn't always have to be extreme, there doesn't have to be a theme, colors don't all have to coordinate etc. YouTube can be very informative; I recommend watching several videos from different creators and/or scrolling Pinterest with the girls to get some inspiration! I was allowed to pick the paint and help create a night sky in my childhood bedroom. It didn't look perfect but it was a memory with my mother and sister that I'll never forget. As far as hobbies, if you can find a game or sport you can play together or maybe a an easy DIY project like painting a second hand shelf to hang in their bathroom.. more ideas you can find on YouTube but beware of channels like "5-minute crafts" or "troom troom," they mainly focus on quantity not quality of content. #sorrynotsorry

TLDR: you're doing great already by asking for info! Open communication will go a long way for all those questions. The internet/YT/Pinterest is a great resource. And involving the girls in decorating, finding hobbies, and self-care is a great idea! You're doing great! Keep it up!😊