@Sleepingdogs12
I wonder if the parent left too much to the step parent and she has realised this now or has she pnd? Yes you'd want things to remain the same for the step children but it really depends on if parents were taking advantage before.
If you have been doing too much and taken advantage of and now you have a new baby, perfectly reasonable to say no to school runs.
The pressure to do a school run with a new baby is a complete PITA.
If they have two parents able to do it, you are not unreasonable to say No more.
Withdrawing everything would be unreasonable if they stay with you a lot, but if YOU have been doing too much then tell their father he needs to do more.
Unfortunately this is the reality with being a step mum, for so many.
Childless young woman, roped into parent children that father wants to avoid doing doing the slog for his children, finds a new young girlfriend to do it for him. Classic.
Then a new baby arrives and new mother is left with it all.
You will need to be very firm if the above is the case.
Usually the mothers end up exhausted, totally taken for mugs, disillusioned and hugely regretful.