I want to know when 'have been' and 'has been' can be used when talking about multiple people doing something because i want to know the answer for a question, but most importantly i want to know WHY. The question is a fill in the blank, "mr smith as well as his wife and daughter________ to their school twice." Have been or has been?And WHY?
The subject is still "Mr. Smith" (note that capitalization is important) so it still takes the singular verb.
The phrases "as well as" or "in addition to" don't change the original sentence into a compound subject. I would also set off the other phrase with commas.
Subject and Verb Agreement | Grammar Rules
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.