Whether a NR child considers themselves part of their NR family isn't only influenced by holidays with that family though, is it?
I imagine (from my own experience) that the RP has a great deal of influence over whether the NR family is perceived as family. Sadly, from posts here on MN and other narratives, it seems that in many cases, the expectation is that NR children are entitled to holidays and treats with the NRP, but should be excused the less appealing parts of family life, such as house rules and shared responsibilities.
I can't imagine it is easy, holidaying with children in a blending family for whom different boundaries, rules and expectations apply. It must be difficult enough for a stepparent to holiday with children other than their own where they may not agree with all the parenting decisions being made. Stepparents must find it a lot harder to tolerate the inevitable reaction to late nights/long haul travel/different accomodation/unfamiliar food than the child's own parents do - and I can remember thinking some awful things about my toddler DD in the small hours of the morning after several nights without sleep in a cramped hotel room, sobbing and begging for her to doze off 
I wonder how many stepparents and prospective stepparents have considered that they may never be able to share holidays with their children and partner together? If finances, contact schedules or court orders prevent the NRDCs participating in a family holiday all together, then the overwhelming opinion seems to be that the stepparent and her DCs should holiday without her spouse, because the NRDCs will resent the family if their Dad holidays without them.
I know there has been discussion elsewhere on this board about the phrase "you knew what you were getting into" - but the reality of that is incredibly complex and potentially life long!