Translation:We are a family and moreover today is a holiday.
It's Italy. La famiglia e tutto. Nothing needs to make sense where Italian families are concerned. It's a separate universe. A universe consisting of (ONE) family. More direct answer - I'm assuming the context is someone saying that it's a special day - we have to spend it together. Of course they spend most other days together as well but there you go - "La famiglia e tutto"
It's hard to explain, but it's correct. I think it's because it describes the whole day (but, being a native speaker, I've never thought about it before). For example, "Oggi è festa" means that today is a day of festivity (as Christmas, Easter...), "Oggi c'è una festa" means that today there's a party, but "Oggi è una festa" sounds a bit odd. It could make sense if you said something like "Oggi è una festa molto importante" (today is a very important holiday) talking about an anniversary or something like that.