<human>: Can you provide a brief rundown of the text in within 3 sentences?

Hi guys!

I need some expert cat advice.

My friend's apartment caught fire, nothing much but there was smoke damage and they'll have to stay with the parents for about a week... and the mother is super allergic to cats. So I said I'd do it. 
She's this really tiny female, adult but kitten sized.

I have a two cats, Truffles [1yr6m] and Nacho [6months, not neutered yet]. They are very friendly with everyone and are best friends with each other. Introducing Nacho to Truffles was really easy because I had a glass door in my old apartment, so they got to hiss and swat at the glass a few times before meeting directly, but when they did it was instant playing.

My biggest worry is that Nacho is not neutered yet, and he's hitting puberty hard, going crazy! Is there a chance he may try to hump her and they end up fighting?

I don't want this to be any more stressful on them than it has to be. SO I have a spare room that I can keep her in, but Truffles can open ANY door in this apartment and I don't have time to get a lock, she's coming tomorrow morning (It's after 10PM here)
<bot>: Please, if you have experience fostering or catsitting, what do you do to introduce the temporary cats and avoid stress for you and them?