No, it could not do so yet the same turn. The group must already have moved in order for the first minion to have ungrouped and be placed on the Source well. A fusion can only be triggered directly after a unit's movement, which it no longer is. The next turn, if the group is able to move in such a way that it ends its movement still adjacent to the minion on the Source well, at that point it would be able to trigger a fusion.
