No you are not being unreasonable, you are on leave, they need to ask someone at the work place now unless your work want to pay you for your time and you agree top it. You trained them, you have answered a few of their questions, now it is time for you to concentrate on yourself and your bubs.

FWIW My work contacted me to sign something which I didnt mind doing but told them that it would ave to wait until it was a time convenient for me which was a month later but I am entitled to my leave.