My Shetland type, around 17 years, has Cushing and EMS. He's been on drugs but is stable now. He's quite perky but I've got boots on him as his feet are a bit tender and he's on bute.
I feel for you - it's never an easy decision.
My Highland, who's 21, has COPD which is worse in summer (along with his sweet itch!!!!).
I may decide to let both of them go together - but it will be weird not having any ponies here.