Before residence is granted, nothing changes: existing status governs what anyone may do. Once conditional permanent residence begins, the spouse and included children hold that status with its rights, including living, working and studying.
Nothing changes until status changes
Hypothetical example: the couple's daughter plans to look for American work as soon as the petition is filed. Filing changes nothing about what anyone is permitted to do; only status does. Until conditional residence is granted, each family member's activities are governed by whatever status they hold, and working without authorization creates problems the later case may not repair.
Once conditional residence begins, the principal, the spouse and the included unmarried children under twenty-one hold permanent resident status subject to the two-year condition, with the rights that status carries. Ageing out or marrying before residence is granted ends a child's derivative eligibility, subject to the statutory age calculation rules, which should be applied to the actual dates. Keep a record of each person's status throughout, because the sequence matters later.