Steve, the Firenzecard will not be a good purchase at all for just these two attractions.
Buy tickets for the Duomo here:
https://www.museumflorence.com
Tickets cover entry to the dome climb (advance time entry reservation mandatory), baptistry, crypt, belltower and museum, You should make your reservations to climb the dome at the same time you purchase tickets or at least well before you arrive in Florence: instructions are on the website. Understand that the dome reservation time also starts the clock ticking on the 72- hr. life of the ticket. You will need 4, €20 full-priced tickets for your family. There is no single ticket just to climb the dome.
Buy timed-entry tickets to the Accademia here:
https://webshop.b-ticket.com/webshop/webticket/eventlist?production=4
Tickets are currently available so go ahead and order them if you know what day/time of day you want to visit. You will need two 16,00 € full-priced tickets for the adults, and 2 "Gratuito/Free" 4,00 € tickets for your children as long as both will be under age 18 at the time of the visit. Bring their passports to the museum with you for proof of age.