Broad answer for “Check if ALL ACTORS” are loaded would be to do a World sized overlap → Get overlapping actors, then do a Loop check. If you know the exact number there should be, then just compare the count.
(All overlapped actors -> Length) == Num
If there’s a specific list then give them all custom Actor Tag.
Get all Actors with Tag, then check length and/or specifics
With world partition/composition you might run into actors outside your current grid/stream distance not being loaded. World Comp streams sub levels based on a streaming distance.