Are the to do and doing objects after the be verb ok?

The component after the verb 1 Be is a slogan, not an object. Both doing and to do can be used as predicative.

My job is to clean the windows. /My job is to clean the windows. Yes

It's okay to use him or her in this sentence, and it's okay to use theirs. A friend in front refers to a general term, not a person, but a kind of person, so it can be used completely.

3. It is best to refer to someone, anyone, etc. with pronouns.

I hope I can help you, but I don't know how to ask questions.