First of all, if you are diving 2 80cf tanks down to 500 psi each, then you probably don't have enough gas to accommodate your deco obligation.
I teach that for OW, you should keep 100psi/10 ft of depth for your ascent with 500psi as the absolute minimum. If your dive takes you to 130 ft, you should start up with 1,300 psi. That gives you 800psi to swim away from the boat, 900 psi to get back to the up line and 1,300 to ascend (on a 3,000 tank) That should be enough for you and your buddy to ascend with a safety stop. The presence of a pony bottle does not change this. If you want a longer dive, you and your buddy should invest in bigger tanks, but be careful about that deco!!!
20cf and 13cf tanks should never be used in your gas planning. They are redundancy in case you run out of air AND lose your buddy. If you are truly freaked out, they won't last very long at all. You don't have the gas you think you do.
40cf and above can be used in gas planning, as long as you plan on deco obligations as well. Any decent deco software can sort this out for you. My Petrel does an awesome job telling me what gasses I can use and when. This is the essence of tech diving and not something you should just play with. Learn it right or leave it alone.