So while you don't 100% HAVE to inform banks, it's always a good idea. That way when your accounts have charges in another country/currency they don't get flagged as fraud and your cards stopped. I've had that happen before and it's huge mess to sort out while away. You'll be traveling with family so I'm sure if that happened you'd be fine, but often travel alerts can be set even online without having to speak to someone on the phone or in person.
It sounds like you are super well prepared. :)