According to this anecdotal Reddit post , salmon oil holds up to 460F, 232C. However, most fish oils are considered unstable and unsuitable for cooking as their Inherent Oxidation Stability is relatively high .
Sprinkle confectioners sugar on silicone sheet before putting down jelly. Confectioners sugar is sugar and corn starch and it will limit adherence. It will not be weird in a dessert.
Do not use silicone sheet. Use a nonstick frying pan. Do all the rest as instructed recipe (in refrigerator etc). Teflon is more unsticky than silicone.