What is the ruling on the prayer of two groups of travelers (Musafirun) when the leader (Imam) of the fear prayer commits an invalidating act before the departure of the first group, and appoints a resident (Muqim) as the successor (Istikhlaf)?

Primary text

If the Imam, who is a traveler leading two groups of travelers during the fear prayer (Salat al-Khawf), invalidates his prayer before the first group departs and appoints a resident as the successor (Mustakhlaf), then both groups must complete their prayers (Itmam) because they are following a resident. If the invalidation and succession occurred after the first group departed, only the second group must complete their prayer because they are specifically following the resident successor.