yes and possibly no
temperature is KEY with ponies - the BEST chance of survival is total issolation. Keeping pathogens to a minimum.
so has this tank been running with a smattering of coral ect that comes through it - does it have LR or a sand bed if the answer to any of that is yes I would say... go buy a new 10 gallon.
You will want to QT your horses for 4-6 weeks - yup you heard me. It takes awhile to get the hang of feeding and checking them, learning what they are like, so I would QT for AT LEAST 4 weeks - EVEN if you have a set up just for ponies.
If you are unsure if they are wild caught or net penned or tank raised - OR had been tank raised, but were put in with wild caught or net penned I would treat them as though they were wild caught - a little reading will tell you what to do as I can't remember off the top of my head. You can treat for bacterias that they most likely have while they are in QT.
an air stone is perfect as well as some FAKE hitching posts - those plastic plants do well. I would keep SG where the tank will be at. bare bottom so you can watch for poo. and I would call your vet and get a prescription for diomax - 250mg for a 5 day course will treat gas bubble disease - ask for refills. A friend once said gas bubble is to
sea horses like ich is to tangs, but GB will kill your ponies so be ready.