Plunge pots into loose soil, fine mulch or coarse sand.

Unless pots are generously sized plants would be much happier getting planted out now, or at least potted on.

Here's what I do with my potted stuff (I'm in west Oly):

The bonsai blue atlas cedar, with a very shallow pot, is put into a crate that was used to store daffodil bulbs in at the nursery I used to work at. Open mesh for ventilation/drainage. I pack clean pine shavings or dry maple leaves around and over the pot. Then it gets shoved under a north-facing eve on the back deck, where it's sheltered from most of the rain, wind, and coldest temperatures - the prevailing winds in winter are from the southwest. The big dangers to bonsai in winter are wind and waterlogging. Temperatures only matter when it's extremely cold, and then only to the roots. The above-ground parts of bonsai can take the same conditions as the plant would take if it were planted in the ground and not bonsaid.

Other potted stuff: the really large bonsai pieris gets left where it is as it's too heavy to move easily. It's been fine for many many winters now, including last winter with all that snow. Broke a couple of smaller branches but that's just part of the time element of the art form. 1- and 2-gallon size pots get shoved under an eave out of the wind. So long as they're up against the house and out of the wind they seem to stay warm enough to not freeze the roots. 5-gallon and larger get left where they are.

Unless your conifers are tropical species, they're better off left outside for the winter, rather than stored inside.

They will be fine outside over winter. Group them together in a location where they can get natural rainfall but won't be overwhelmed by it. Local nurseries leave their potted conifers of all sizes outside through winter without problem -- you can too.