just posting a thought from a stepmother, who has been in a similar position.
dh's ex always said that when the dc were with us, they were his reponsibility (fair point, tbh)
BUT, dh travels a lot. and so some of the time they were "his" responsibility, they were actually mine, iyswim.
and that meant sometimes talking to teachers, sometimes popping to the doctor's/dentist's/etc with them.
all fine, until ex realise dthat things were going a bit too smoothly, threw her toys out of the pram, and insisted that all these people had nothing to do with me, as I didn't have PR, whilst also refusing to go see school for a meeting as it was dh's time, or not wanting to take time off work for a doc's appt, as it was dh's time etc.
PR for me would have made our lives a hell of a lot easier, and, to be frank, my step-children's lives a lot easier too.
But dh's ex said "over my dead body", and so we carried on, with the children asking me to speak to school about something, school having to refuse to speak to me, us all jumping through hoops for a while, with dc getting increasingly upset, unti lex decided to front up and "save the day"
sometimes, as much as it hurts, it might just be the best thign to give a step parent PR. for the sake of the children.