This would be pretty normal behaviour -- it is one thing for Sam to enjoy meeting a dog who is there for a visit, but they do get jealous as soon as it becomes clear that the new dog is sticking around. They need to figure out who is the top dog and to a certain extent you need to ignore this and let them have a few scuffles, keeping an eye out so that it doesn't get out of hand. This may well include some noisy fights that seem much worse than they are. If you intervene each time, they stay unsettled as their relative positions are not assured.
That said I would be very careful about toys and feeding, which tend to be the hot spots -- because it's better not to create situations where problems might arise, and they will sort out their roles anyway over time, and will be less likely to actually fight it out later on. If there are toys that keep causing fights (in my house, it was chews when I got my second adult cav) then do not offer those items at all, or offer only while crated or under controlled supervision. I'd certainly be feeding the dogs a good distance apart at least for a while, or else in their crates.
Almost certainly you will find the relationship has settled enormously by the time you go away. Also as two among five dogs, the situation will likely be diffused anyway -- lots of dogs to play with, with less focus on one having to watch the other. I'd just ask your friend to follow the cautions above regarding feeding and toys as well.
My guys gave each other a few good bites in small battles in the first few months after Leo joined the house, even though they were also friends almost immediately. Now this tends to only happen when Jaspar, the stinker, plays games with foods and toys -- he likes to set them up so Leo tries to take them, then he'll try to snatch it away just in time. Every now and then this leads to a skirmish still. :roll: