Can I add both at the same time? Top dress with 2/3 cup of each and water in?
2/3 cups- total per plant (not 2/3 of each), what you could do is try grinding them up really well mix it in your water and water them. Just make sure it's not sitting in the bottom of the water jug.
I wouldn't use bone meal, very high in fluoride, and probably other bad stuff, considering the junk they feed animals. The yellowing could just be lack of light due to growth of upper leaves.
Is there a better way to supplement P flowering stage?
By itself, I don't know. I just use complete hydro ferts. I don't think bone meal is even that good a source. It's calcium phosphate, which is pretty insoluble. I guess you need monopotassium phosphate. For calcium and nitrogen; calcium nitrate.
Just looks like normal bottom leaf die off from shading. You'll have lower leaves dying off quite regularly as top growth shades it out.
