I agree...first thing to look at is your source of UVB. Getting light through a window won't provide it as most window glass blocks UV. You can hang a fluorescent tube fixture with a ReptiSun 5.0 over your Hoya...but I'm sure you realize that they won't be able to live on that plant as they grow. Veileds are too territorial to share living space. They will need to be separated visually. Eventually one will become dominant and the subordinate cham will break down with health problems first.