Well, since both horses in the pasture sound like that it's likely that you are dealing with an infectious respiratory disease. Viral respiratory infections start out with clear nasal discharge. Since Equine Herpes Virus causes 80% of upper respiratory infections in horses, there's a good chance that that is what you are dealing with. (EHV is highly contageous and can lead to more severe problems than just respiratory infection so it's not something to take lightly. Remember all of those quarantined barns and racing stables---horses with neurological disease? Mutated EHV.)
It would be a good idea to move both of these horses in out of the rain and quarantine them from any other horses on the property. Check temperatures and watch for any fever as well as watching for symptoms to worsen. It would also be a good idea just to call your vet and give him a heads-up on what you are seeing.
Licensed Veterinary Technician