There are always as a minimum four professionals involved in each phase of a functional safety lifecycle. For each task one professional does the work. One independent professional verifies the work. One sufficiently independent professional performs the assessment and one professionals manages all of this. This does not mean that each professional spends equal time on a particalur tasks. Not each functional safety tasks will cost you 4x times the man power. If you do it right it is much less.
So four roles: