Say Dad and SM have a young child together, and dad has his daughter from a previous relationship. Dad and SM have decided that they are a united front in front of the children, even if they disagree behind closed doors. Ex: Dad disciplines the younger child that they share, SM (bm in this situation) doesn't agree, but continues to follow through to teach the child that mom and dad are united. They then discuss the discrepancy behind closed doors.
How does this transfer into a step child/ step mom relationship? SK acts up and BD is in the bathroom or out to the store etc. SM says "That behavior is unacceptable and you need to go to your room until your father gets home" or something along those lines. If the BM of the SK heard about this and was angry that SK was "disciplined" by SM, would she be in the right? What about the perspective of the bio child of both parents. At certain ages, it is not possible to explain the difference effectively. You can try but...they still see the behavior and learn from it. I'm talking about a toddler, if that makes a difference.
My real question is should BM be able to say that SM does not have ANY say over my childs behavior in her dads house, regardless of their house rules? Is that fair to show the younger sibling that its not equal? Does it matter?
This is all hypothetical.