I don't ship Wolfstar but I can definitely see Remus doing Sirius' hair. Also lets all just take a minute to picture Sirius' hair in a fancy braid. And Lily. Imagine Lily teaching Remus using Sirius's hair.
Harry Potter was saved by a mother's love more than once. Harry may not of had his mother but he had a lot of comfort from mother like figures. Whenever Harry needed comfort it was always from a mother figure.