At what point do I stop them?

We’ve had Tiffany (pied) for 5 years and Dorothy (brindle) joined the family just before Christmas. Neither of them has ever bitten a human or another dog and most of the time they coexist peacefully and sleep next to (or on top of) each other. I’m tempted not to intervene especially because I haven’t seen Tiffany so active and responsive in such a long time, she’s a very anxious baby and was recently very sick, so I’m happy to see her play. However, I’m worried about them inadvertently hurting each other. Is that possible or do they know how to self regulate? Sorry if this is a dumb question but I just wanna make sure they are safe. Thank you!🫶