Most importantly to start with.
Call a rescue organisation, explain the situation, say you need them picked up urgently.
You need to contact the owner, find out their dietary needs (what they need to eat and in what amount), find out their medical history, when they were wormed etc. Everything he can tell you.
If he can't give you any definite dietary guidelines, I would advise you feed them haylage only (or hay if haylage is unavailable) and make sure they have plenty of clean fresh water. Horses can be killed by inappropriate feeding but I'm sure they all need plenty of hay or haylage.
Honestly, I wouldn't call a vet, vets can be extremely expensive, if a rescue organisation can come and get them, advise them that the horses may need veterinary attention and they will provide that for them. You are not an experienced horse owner.
I would strongly advise that you do not take on these horses, instead ask the owner to hire a trained, professional groom (stablehand) to come and take care of the horses untill they can be rescued or sold/rehomed to an experienced owner.
I know it maybe sounds great, it's lovely to have a horse but you appear to be nowhere near experienced enough to take care of these horses. Make sure you do what is best for these horses, they need professional veterinary care and experienced ownership.