I play Malzahar and Yorick often and I think Yorick's ghouls are in a good spot. Yoricks ghouls always prioritize champions, so I can E a minion for the last hit, and the ghoul goes straight to the enemy and starts harassing.
Malzahar's voidlings are very powerful, especially since they get 100% of your armor penetration and a 1:1 ratio with your bonus AD. The only thing I wish was changed, is that sometimes when there are no minions in lane the voidling just sits there, pretty far from you and it takes him a while to start following you. This is when the enemy mid just pokes your voidling and kills it, forcing you to summon another to help you clear the next wave. It's as if the voidling hesitates before starting to follow behind you.
Also, I would love to see your pets be treated like champions under turrets. That is, the turret doesn't target them unless there are no minions or they've struck the enemy champion while under its range. I am not entirely sure what effect this would have, though I could see AD Malzahar just obliterate towers. I'd love to see it, but it would probably make these champions too strong at siege.