Condition stacking on multiple skills
You can stack multiple stacks of bleed with the shortbow/sharpening stone/crit/earth sigil, yeah. That’ll get you up to 4 stacks of bleed in one go! I’m not sure what you’re asking about burning since I’m not familiar with the sun spirit passive, but I’d take a guess that it’d add both the bonfire burning and the sun spirit’s burning.
Generally it’s a good idea to use skills and sigils that work together!
It would add 1s of burning from the finisher and 3s from the spirit.
bleeding stacks in itensity and burning in duration.
If you hit your foe’s back with the shortbow, while sharpening stone is active, sharpened edges traitet (and procs) and the shortbow has the sigil of earth (and procs) you’ll apply 4 stacks of bleeding with 1 shot.
If your torch 4 skill applies 6 seconds of burning (just an example) and the sun spirit 3 seconds, the 3 seconds will be added to the duration, meaning 9 seconds of burning.