None of my dogs are new, or young! However, Molly has recently decided she wants to share Sallie's bed (sometimes) Sallie is usually ok with this, but Molly the Princess doesn't always respect boundries, so there is occasionally some grumbling. I let them work it out unless it seems to be escalating, then I tell them to "knock it off, be nice", and they do. I direct it at both of them equally, unless I see one (ok, Molly ) being a butthead. Like the time she was trying to lie down in a space that was way too small for her, and nesting , and she stepped on Sallie. Sallie growled and barked, and I went and got Molly and made her move off the bed entirely.
If it's just grumbling, I'd let them sort it out.