You don't need a head lamp marker if as you have forward facing markers on your mudguards.
I will say that they need to be bright! (Not for the regulations) Because if you ride at night oncoming vehicles will find it hard to see them and assume your a bike with the obvious consequences.
Twin headlamps must be one dipped one main for the SVA if they are closer than 500mm (I think) edge to edge
Unless you mount one above the other.
If your Trike is more than 1700mm wide but less than 2000mm you must have twin headlamps and the outer edge of the illuminated surface of each lamp should be no more than 400mm inside from the widest part of the vehicle. They can then operate together.
