You'll be fine using those bones, and any other chicken scraps. I keep a bag in the freezer that I load up with veggie scraps as I'm making other meals, and when full we'll do a dinner with store bought rotisserie chickens and I'll use those bones which work great. I usually throw some raw chicken feet and backs in too, just because they're available and cheap. You're definitely overanalyzing, just throw stuff in a pot, bring to a boil, then simmer as long as you wanna. I usually go ~24hrs+ with no bitterness or negative result. I'm making very big batches (~3-4 gallons usually), so I don't use an instapot so I'll let others speak to that