I think it is fine for a parent to meet up with each of their adult kids a few times a month to do something nice together (ie. grab breakfast, lunch or dinner, go see a movie, or both, or get an ice cream or coffee, or both, or do all of those things at once). I know my sds will want to see just dad sometimes as adults and I will wholeheartedly encourage it for these reasons:

1. Let's face it. Stepkids don't want relationships with us (most of the time). If they are nice to the SPs, it is to keep things peaceful with their parents.

2. We don't want to see them all the time either. If Dad visits them out of our homes, it is less stressful for us. Often, anyway.

3. Skids shouldn't bash sm to dad and dad should not bash skids' SOs/spouses to them. In fact, when dad and skid are hanging out together, they shouldn't discuss each other's sos. At all. They are there to see each other, and work on their relationship with each other.

4. I think its fine for dad and skid to email/call each other and say, "Hey dad/skid, do you want to grab dinner with me then go see Skyfall?" That is polite and to the point. Most people would take that as an invitation to hang out with their loved one , just the two of them, even apart from spouses/SOs. And most wouldn't be offended by that type of invite, including SPs. I don't need to be present every time dh does something with each of his kids.

5. But to try to dictate where a fellow adult can/cannot go is wrong, unless said adult truly has done something to deserve it. To say, "Hey Dad, don't bring sm when you come to the restaurant to meet me for dinner/Skyfall" is wrong.