Depends on the context. My DH and I have 6 kids, aged 10-20. We don't differentiate between which are whose when they're here, unless it specifically involves their other parent or home (e.g. relating to parents' evenings etc or arranging holiday switchovers).
Mine live with us full-time so we often do things as "the 5 of us". They visit their father alternate weekends and 50% of the school holidays. My dh's kids have the same arrangements with him, officially, although they often have sports events, trips with friends etc so the schedule is more flexible, but we regularly have weekends and holidays with all 6 (plus the 20yo's girlfriend he now lives with), or any combination of them.
They all get along great and refer to each other as their brothers and sisters.
My kids are also about to get a half-sister as their father's new partner is due any day now. She's really lovely and I'm happy to know my kids are being loved and cared for on their weekends away from me. As long as we avoid discussing anything financial in front of the kids, XH and I get on fine now. We even attend our kids' sporting events, dance shows etc together, with our current partners, which I know my kids really appreciate!
XH and I failed to make our marriage work, but I like to think we've made a success of our divorce 