Start at what ever you can pull comfortably and can adjust up for the future. Most bows are only good for 10 pounds.

Pulling a trad bow is much different than a compound, there is no let-off on a trad bow. They are harder, or feel that way, because they are ment to be snap shot and not held drawn like a compound.

Try your brother-in-laws bows and see what your spindly arms think.

Or more correctly, your shoulders and back, that is where the power comes from on drawing a bow.