Hello gEOrgEkUng
1) YES. With the exception of mountain excursions. See the validity map:
https://sbb-tickets.cc/en/tickets-offers/travelcards/area-validity-map.html
2) NO. The Family Card is only available for Swiss Travel Pass or Swiss Half Fare Card holders. In your case, you can purchase the Junior Card for CHF 30, valid for 1 year, at the SBB travel center (for tourists, it is not available online).
3) NO. Day Passes cannot be combined with international fares. You need two separate tickets to/from the border. Or, get yourself an international ticket from a station in Switzerland, it can be the cheaper option.
Kind regards,
Roland