We have always had 3 books and no more, and recently this has been dropped down depending onthe length of the book (some are very long!). And then she has 2 songs, one in bed and one out of bed.
Has he only recently started pre school? if so there may be some separation anxiety. We have had a similar phase tho and we used various techniques to deal with it, but if we say Daddy is doing bedtime then that's what happens, once they work out they can control what goes on then you are lost

. On the odd occasion that she starts playing up when I leave now I gently but firmly tell her that I'm going, and that I'll be back to check on her in 10 minutes (and I make sure I keep my promise). Repeat to fade! or DH takes a turn.
He may be getting ready to drop his nap as well, worth considering.