There's info on Senvelgo here:
Info - New Treatments for Feline Diabetes Few people here on FDMB use it but we can still help you.
Is the ProPlan and Tiki Cat dry or canned? A canned food only diet that is low in carbs is best for diabetic cats and it's possible to feed a multi-cat home the same food without going broke. Your non-diabetic cats can benefit from a low carb canned food diet, too. Food that is too high in carbs is the reason why many cats end up diabetic in the first place.
The canned food charts are here:
Links to FOOD CHARTS
A newer US chart:
Cat Food As-Fed Chart
Any food under 10% carbs is best. There are many brands to choose from: Fancy Feast pates, Friskies, some of the Tiki Cat, Blue Buffalo, etc What your cat likes to eat and you can afford is fine. For mutliple cats, many people buy a brand that is avaialble in larger 5.5 oz or even 13 oz can sizes and split a can(s) between all the cats. Other people buy cases of food.
Your diabetic will need to eat multiple small snacks daily in addition to breakfast and dinner. The snacks will keep blood glucose levels stable, kind of like how Human diabetics often snack on healthy things in between meals. There are microchip feeders you can get that will only allow your cat wearing the special microchip tag to access the food.
If you have to feed some dry, the only suggested brands that are ok for diabetics are Dr. Elsey's and Young Again. These are expensive, though. If you have to feed the non-diabetics a more affordable brand, then keep the diabetic away from it. We can suggest ways on how to do this.
Did the vet give you any information on testing blood glucose levels daily, either with a meter or a CGM?