Peaceful dog sitting

Bells21

A family member is going on holidays in a number of weeks for a few days and has asked if we can dog sit for them. They have a neutered female Yorkshire terrier approx 10 months. We have a male JRTx and a female schnauzer both are neutered. Our JRTx isn't a fan of having other dogs(apart from our other dog) in his space and will bare teeth and growl. We have started walking the three of them together to get them used to each other and he isn't bothered by her on these walks. He had quite a few sniffs of her rear end and she seems to be accepting of his signals(him asking for space) and while still showing some interest in him, is giving him plenty of space. A few times on the walk our fella went close to her and brushed off her as he passed which is usually where things spark and he didn't react so we rewarded him.
I'm looking for anymore advice as to how we can make the few days stress free for everyone.

Latatian

Don't leave them together. If you're not directly supervising- as in, in the room, paying attention, and not distracted- then keep them separated. Different rooms, crates etc.

Forgot this one today for literally under five minutes. Those five minutes cost me three hundred quid and more to come.

Bells21

I definitely won't be leaving them unsupervised, we have baby gates and crates in different rooms and they will be sleeping in separate rooms.
Thankfully we have enough space that we can keep them totally separated when/if it's needed.