What to do about dogs who aggressive towards my dog?

I'm watching 2 golden retrievers one is 5 the other 2. Overall they are pretty good dogs but they are being alittle aggressive towards my dog. The 5 year old seems to constantly growl and step at my dog, whether that be getting close to him, if he trys to play with a toy or if he goes near his brother. The 2 year old seems to be good around my dog although he has tried to nip at him twice when my dog jumped on the couch to lay next to me or if we are playing and my dog trys to play with the toy as well. I have them separated and informed the owner, the owner had stated that they very friendly towards other dogs and that they just need some time to adjust. I know being in a new surrounding can be scary and take some time getting use to but was wondering what else I could do as I am watching them for another 5 days. My dog is 1 and he still has that puppy energy so he wants to play but hes been really good at keeping his distance and is very friendly towards both dogs (even though they have not been so nice to him)