Help adjusting cat to new surroundings while cat sitting.

Hey everyone I'm new here and having a bit of a problem. I have two cats and they are fine. However last night a friend of mine needed a fast favor and needed me to watch their cat. Long story shoot I have another cat I'm watching now and did not have the time to properly introduce him to his new surroundings me, and my two cats. The poor thing has already been shuffled out of his home and now he's here with someone he doesn't know in a place he doesn't know with 2 strange cats. Obviously he's not taking it well. I need some help getting him comfortable here for the next week until his owners can find a place to have him more permanently. I have them visiting him tonight to help comfort him any advice would be welcome. 

You may think that you'll only be sitting for a couple weeks, but it still makes sense to take the time to make proper introductions to the environment and the resident cats.

Do you have an extra bedroom or bathroom you can set him up in?  It might seem uncomfortable, but it's better than having him get into fights with your cats, peeing all over the place, or hiding in tight, inaccessible spots.  It will give him a space to become comfortable and claim as his safe place.

After a few days, put your other cats in another room and allow him to explore the house under supervision for short periods (30 mins at a time). 

After a few more days, allow for introductions to the other cats.  It will probably still be stressful, but he will find his safe place if it becomes too much. 

maybe give him treats and play with him

I'm a little space constrained right now. The best place for me to do that would be my patio but its a little cold at night here. I could make him a bed out there it gets to 55 here I'm in florida is that too cold?

I know outdoor cats and strays can take much colder weather, but my pampered indoor cat starts huddling under the blanket when it gets to 65 here.  Would the bathroom not work?

If nothing else, the patio will probably do as long as the cat can't escape, you spend time with him, and it's safe and quiet.  

Both my bathrooms are used by people I have maybe a day that bathroom  tomorrow night I wont be able to stash him there without people using that bathroom.