Shared load posts & notches for deck/balcony/roof

Hi,
I’m trying to wrap my head around shared load posts. I think this usually comes up when building a deck a with a roof. Or, as in my case a bit more complex: a deck with a balcony on top that has a roof. The only info I have been able to dig up on the subject is this article:
https://www.decks.com/how-to/articles/how-to-use-shared-load-deck-support-posts
Which is a bit a light on the details. I was wondering if someone could fill in some details?
1. How can I adjust the load bearing capacity of a post after notching it for multiple beams? in other words, can a 6×6 still hold 10,550 lbs @ 14 feet, if it has a 1.5″x9.25″ notch removed and filled with a 2×10 beam in the middle? Or do I need to treat it as a 4×6 for load bearing capacity above the middle notch (8425 lbs @ 14 feet)? Does it matter if its notched 3 times (deck, balcony floor, balcony roof)?
2. When calculating load for a roof on top of balcony, on top of a deck, how should I add up the loads? deck requires 50 psf, balcony + roof requires 100 psf? does that mean my posts need to support 100 * tributary area of balcony + 50 * tributary area for the post?
3. Is it silly to try to use a single post to support a deck, balcony & roof? Is there a better way? (single post for deck+balcony & separate post from balcony joist to roof? one post for deck, a different footing+post for balcony + roof? one post footing -> deck, another post deck beam -> balcony, another post balcony beam -> roof)
To give a straw man example to discuss:
Say I have a 10×5 balcony 10′ above a deck. The deck has a center beam @ 5′ and a perimeter beam @10′. The beam is sitting in a post notch 4′ above footing. The balcony has a roof that is supported by a separate 4×4 post bolted to the balcony joists.
– tributary area for single balcony corner post: 5*2.5 = 12.5 sqft
– tributary area for single deck post: 10 * 5 = 50 sqft
– combined load: 12.5 sqft * 100 psf + 50 sqft* 50 psf= 3,750 lbs
– 6×6 can handle 10550 lbs @ 14 feet, which is > 3,750. So all is well?
Thanks in advance for any and all advice.