Hi and Welcome, to the one place you never want to be but will be so glad you found.
Most kitties don't like the prescription DM food for very long, and it is completely unnecessary. I personally have 11 cats only one of whom is a diabetic, and everyone here eats exactly what my diabetic eats, just good old fashioned Friskies Pate Flavors. You can check here for commercial foods that are really better in quality than the DM that Mylo might like better
http://www.felinediabetes.com/diabetic-cat-diets.htm Just want to keep his carbs under 10%. You don't have to feed both cats a different diet, his buddy can eat the same diet as Mylo, I know even my non-diabetics are in better shape since the diet change to regular old Friskies. Dry food isn't really very good for any cat, and really not good for a diabetic.
Other things that can sometimes get a kitty to eat:
Trying warming it in the microwave
Sprinkle with parmesan cheese
Add a little Tuna juice
Sometimes even letting them lick a few bites off your fingers will get them started.
Also which insulin did they start Mylo on? Most like a consistant dose, every 12 hours apart, not one dose in the morning and a different one in the evening.
Lastly if there is one thing we will nag you about is learning to test him at home. It is very easy once you get the hang of it, and we can teach you how.
Others will be chiming in shortly I'm sure with tons of other questions and links to info. You are now in the best place in the world to help you help your furry buddy Mylo, and we will help hold your hand and paw as you learn to do the Sugar-dance.
What right now probably seems very overwhelming and scary will soon be like brushing your teeth in the morning, just routine.
Mel, Max & The Fur Gang