Nat,

Different species like different amounts of water, so first I'd suggest you study up a bit on the species you're growing. The rule of thumb is the more succulent the leaves, the drier you can let it get. But I never let mine get as dry as my true succulents (I call Hoyas "honorary succulents", and of course I'm not referring at all to the thin-leaved species...) I use the "feel" method - if the top 1/2" of soil feels dry, I water it. So in summer, that may be every couple/few days, and in winter it may be a week or 10 days.

Denise in Omaha

You can also stretch out the period between watering more if they aren't actively growing. It's easy to overwater in winter and it takes longer for them to forgive you. If it's one of the more succulent Hoyas and it's not actively growing, I let it get QUITE dry in the winter. Some Hoyas will get considerably angry if you water them too much in the winter, trust me. Particularly if they're not getting a lot of light, as was my case last winter.

As Denise points out, some specific research really is neccessary, although heuristics will help you hobble through.

And they also are in locked rooms and are getting poor ventilation

If you know that excess moisture is going to be a problem, then you really need to focus on using a porous soil. I don't use any peat in my mixes, just gritty components like orchid bark, Turface, granite, pumice, etc. This way the mix is still well aerated even when saturated. Putting a small fan near your plants may help as well.