My write-up assumes a "Pony-centric" campaign world based on the current show. As One Tin Soldier just pointed out, Ponies in the show adapt to interacting with objects surprisingly well, which to me indicates that their hooves are extremely flexible compared to those of real-world equines.

Here are a couple more examples, holding a mug and holding a spear:
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I think for simplicity of the rules, one can assume each fore-hoof counts as a hand and each hind-hoof counts as a foot (this way it works out with magic items too). If a particular GM wants to mix Ponies with humanoid races, I'd leave it to them if they wish to impose a disadvantage on using hooves to manipulate small/fine objects.