Tips for Introducing a New Dog?

My wife and are temporarily taking in her brothers dog this weekend (divorce fall out) and are looking for guidance. Currently we have a full size Shih tzu who’s 4 years old. The puppy we’re taking in is also a Shih tzu, about 5 lbs smaller and under a year old.

A few things I’d like to know are…

Best way to introduce them?

We are only going to be this new dogs family for about 6 months at which time the in-laws will be taking him permanently. How will this affect the dogs to get them comfortable then to separate them?

Any other tips are welcome as well!