Would it be ok to add my cats' supplements to their food in the fridge?

My cats are 15, and one is turning 16 in July. Due to their age, they need a gut health mix of prebiotics, probiotics, and enymes to avoid vomitting and also get 500 mg L-Carnitine and 250 mg Taurine due to their age as a heart disease prevatative and need a small quantity of eggshell powder since they get partial raw and won't eat bones. I also give organic apple cider vinegar, b complex, and salmon oil but I can just keep giving those via syringe. I will also be adding RNA, Resveratrol (derived from Japanese knotweed, not grapes) and Cod Liver Oil when I get my next check, plus Syn-flex and msm for my arthritis kitty, as well as possibly vitamin e for their weekly steamed salmon day, and possibly some other things from Pitcairns healthy powder like soy lecthin. Currently, I mix up all their stuff in a shotglass at night with a little water to thin it and syringe it to them in 1 mL increments once every ten minutes to avoid upsetting their stomachs, but it takes over an hour and is stressful for them. They would eat most of it on their own if I mixed it into their daily rations and just supervised to ensure the right cat got the right portion, but they eat tiny amounts many times a day and I don't know if it would be fridge stable. Thanks!