People always present SC responses on MN as if they will be universal and as if how they adults around them respond and frame things won’t make any difference.
The problem is often that people are determined that step families should be as close to nuclear families as possible. And that SC will feel terrible if they aren’t embraced by a whole lot of people who are related to their stepparent. But children can totally understand that there are a whole set of different relationships and that it’s not excluding them if their stepmum’s uncle Brian doesn’t write their name in a card.
Helping them to see that their family includes lots of people that aren’t in the father’s household and that people in that household have different families that don’t include the SC is fine. It isn’t hurtful to be open and acknowledge actual reality. The problems often come when people pretend the stepfamily is just like a nuclear family.
‘Oh, that’s from moira. She’s someone SM knows’ is a fairly neutral statement. Especially when embedded in the understanding that the SC’s maternal family don’t include the members of the father’s household on their cars either.
Where children feel left out or marginalised, it’s not because their name isn’t on a card. It’s the wider dynamic. And concentrating on the superficial stuff won’t actually help. It may even divert attention from the actual problem.
Where there isn’t that wider problem SC are probably less likely to care if their name is on a card or not. Or even check. It only matters if the SC are feeling insecure. And the response to that is to fix the real problem not some superficial symptoms (that may actually be referred symptoms,
But people on MN like to grasp on to the simplistic stuff and decide that the SC feel the way they do because of it. Funnily enough, making the surface change can just push the problem further under the rug.
In this case, the problem isn’t even the SC’s feelings. It’s the OP’s DH’s feelings. It’s not uncommon for people, particularly NR fathers, to have not properly embraced their new complex, stepfamily set up. So anything that reminds them that they don’t live with their children from a previous relationship and their wife has a life with parts ghat are entirely outside of his children feels upsetting. The answer is not to brush that under the rug either - it’s to talk about how everyone can be comfortable with how things are (not how they feel they should be).