Has wobblers syndrome ever been veterinaty diagnosed in this individuals horses? I would talk to him and find out who diagnosed this (in both horses) and how. Get as much informaiton as you can.
Good information about wobblers syndrome: Wobbler Syndrome or Cervical Vertebral Stenotic Myelopathy in Horses
I don't think wobblers syndrome itself is contagious, no one particular cause has been identified. There is talk about genetics being a factor, as well as proper nutrition through pregnancy and development. I wouldn't say its contagious.
I'm wondering if your father is maybe worried about a viral infection? Which there are diseases that can present itself with neurological clinical signs. Examples EEE, WEE, West Nile, herpes virus (nEHV-1) or possibly EPM. EEE, WEE, and WN are carried through mosquitos. EPM through opossum (when horses ingest fecal material containing infection sporocytes). NEHV-1 presents
With other signs including fever, loss of appetite, lethargy, nasal discgarge and other respiratory signs (which are more classic then neurological).
I'm not at all trying to scare you but the main thing is going to be being aware and informed of equine diseases, use an effective vaccinaiton protocol and feed storage practices are going to be good preventative measures. You can talk to your veterinarian if you have concerns about keeping your horses where they are.