The gelatin layer on film is not bromide, gelatin is a protein based organic emulsion to hold silver bromide ,(and other silver salts called halides), crystals in suspension on the film.
Unless you had a very strong thiosulfate solution or left the film in for a very long time it does not normally strip the gelatin off the film. It simply forms a water soluble complex with the unexposed silver salts to remove them from the gelatin.
The gel is left behind to hold any image bearing, (exposed and developed), silver. Since your film was never developed the thiosulfate will remove all the salts and the exposed silver that has been turned to metallic silver.
Your precipitate should be just the various silver salts, (bromide, chloride mainly), metallic silver and whatever drag out from the metal you used to precipitate with. In your case both iron and copper if I read your posts correctly.
https://en.wikipedia.org/wiki/Gelatin_silver_process
"The fixer, typically sodium thiosulfate, is able to remove the unexposed silver halide by forming a water-soluble complex with it. And finally, a water wash sometimes preceded by a washing aid removes the fixer from the print, leaving an image composed of silver particles held in the clear gelatin image layer."
https://en.wikipedia.org/wiki/Gelatin#Technical_uses
"Gelatin or gelatine (from Latin: gelatus meaning "stiff", "frozen") is a translucent, colorless, brittle (when dry), flavorless food derived from collagen obtained from various animal raw materials. It is commonly used as a gelling agent in food, pharmaceutical drugs, photography, and cosmetic manufacturing."
The gelatin, being an organic protein, can easily be burned off by roasting the precipitate. (If you really have it present, I don't think you do.) You don't need to incinerate, just a low dull red glow is hot enough to carbonize the gelatin, as well as oxidize the silver salts. Do this with the lid off the pan and stir it a bit to expose all the precipitate to the air.
I think you have a mixture of silver, iron and copper. I would start by measuring out an certain amount to test with and put in hot HCL ONLY, no nails!
I think the solution will turn either bright yellow, (iron dissolved), or green, (copper). Repeat this in clean HCL until the solution stays clear and the precipitate is off white and fluffy which will be silver chloride you can convert to metallic silver by either the sugar/lye or battery acid/iron method.
