The Baines family with Marty McFly

"The dining room was already half-filled with people. Seated at the table, ready to pitch in, were Milton, twelve, who was wearing a Davy Crockett coonskin cap; Sally, six; Toby, four; and in the playpen on the floor, eleven-month-old Joey. / Stella made the introductions. Marty was utterly fascinated, seeing his aunt and uncles looking so different."
—From Back to the Future by George Gipe (quote, page 105)

The Baines family in Hill Valley consisted of Sam Baines, his wife Stella and their six children.

                                 Sam Baines + Stella Baines
       |               |             |             |            |            |
Lorraine Baines  Milton Baines  Sally Baines  Toby Baines  Joey Baines  Ellen Baines
 McFly family

The Baines family celebrate Joey's release from prison together in 1986

Issue 5 of Back to the Future: Citizen Brown mentioned a member of the family, Albert Baines, as judge of the Hill Valley Science Exposition, though he was replaced with Erhardt Brown due to "ailing". His place in the family, was left unspecified.