Noseweights and cycle carriers

Need some help understanding the relationship between noseweights, towbar weights and cycle carrier weight please.

i can match my caravan noseweight to the requirement of my towing car (70kg), but my towbar also has the facility to mount 2 cycles on vertical struts, the base of which fit into the towbar. The combined weight of 2 cycles and struts is around 37kg. So a few questions:

1. Do I need to add the 70 to the 37 to get the overall downward weight on the towbar, which of course would exceed that recommended for the car by some way?

2. How do I know the maximum weight capacity of the towbar itself (if, say, I changed the car to a higher nose weight capability)?

any help gratefully received.