At the first meeting, because their needs can change the sequence. An eligible spouse and unmarried children under 21 may seek L-2. A spouse in valid L-2S status is employment authorized incident to status, and an EAD is not universally required; children are not work authorized by L-2.
Let household needs shape the order of work
If the household expects two incomes, or a child is finishing a school stage, that affects when travel makes sense and which questions must be resolved first. Record each person's citizenship, current status and travel documents at the outset, since routes differ by nationality and L categories are not limited to Canadians. Keep the dependants' plan attached to the principal case rather than treating it as paperwork for afterwards.
There is a further reason to raise the household early rather than at the end. A dependent's requirement can change the order of the work: a child finishing a school stage may argue for a later filing, while a spouse's professional registration renewal may argue for an earlier one. Those are legitimate inputs to sequencing, and they are cheap to accommodate at the start and expensive later.
Record each person's citizenship and current status at the first meeting as well, since routes differ by nationality and a family member's own history can create steps that do not follow from the principal's case.