Kuhli loach will be fine, I keep Clithion Corona (Horned Nerites) alongside around 8 Kuhli's without problems. Kuhli's are probably the most placid fish you could ask for so no problem there.
Although i haven't kept Yoyo's before i do see alot of people on other forums, mainly Facebook, recommending these to people that have a pest snail infestations to help clear up which i personally think is wrong but there you go!
Also my tank temp is 24c but your discus tank will be considerably higher than that so you'd have to check they would be suitable in higher temps
“Mystery” and Apple snails are quite sensitive to damage - bitten antennae often lead to reduced quality of life and even death from subsequent bacterial etc infections
Yo-yo loaches are just not suitable companion fish to any snail ... even MTS
(but I’d also not keep them with discus, even in the discus manage Life With Loaches, they’ll live much “happier” without - and most Loaches will prefer longterm living at “lower than discus” temperatures)