Dawood can be easily killed with a boat(along with shah) Maelstrom can be killed via poison,The twins for saso are some of the worst targets,alng with tyson willams,and colorado in general.Hitman 3 has very few hard targets,but royce might be the hardest out of the ones you listed

Probably the Twins, but honestly Colorado will always be hardest. On master it’s a freaking nightmare