That is a household decision, but the immigration facts are that the spouse would be work-authorized as an L-2 and the children could attend school. A short assignment may make visits more practical than a full move.
Match the family plan to the length of the assignment
L-2 status for the spouse and unmarried children under 21 gives them residence for the same period as the engineer's L-1B, the spouse is authorized to work incident to status, and the children may enrol in school. Those facts make relocation possible even for a short commissioning assignment. Whether it is sensible depends on the family.
An eight-month assignment that crosses a school year may not justify moving children, and a spouse with a job in Mount Pearl may prefer to visit. Family members who visit rather than relocate enter as visitors and must not work, and a spouse who would like to take short U.S. contracts during visits should obtain L-2 status instead of relying on visitor entries.
If the assignment is extended into a longer role that still uses the specialized knowledge, the family can change plans then. Decide the family question after the petition is approved and the actual assignment dates are known, not on the basis of the first estimate.