Is "be my guests" correctly used in the following case?

"Be my guest" is an idiom that's usually used to (politely) give permission for someone to do something.

If you want to edit my manuscript, be my guest.

Can I try out your new TARDIS? Be my guest.

It indicates the other person should feel free to act as he/she pleases.

In your question it appears the idiom is being used both figuratively and literally, B is inviting A into his house (as guests) and giving B permission to ask questions.

The only questionable bit is the use of guests instead of guest. As far as I know, "be my guest" is the conventional idiom, though given B is referring to a group of people, the the plural form is perfectly acceptable.