Are they dormant ? How big are they ... in pots ?

No, they're not dormant. I'd say they're medium size plants in pots.

I'm assuming it's an unheated garage (and I totally understand z5 - lol!), so if there's a window or some light in the garage they should be fine for a short while. The garage is probably very cool/cold, so you shouldn't need to worry about watering them unless they get very dry.

Probably okay in the garage provided it does not get super cold. You may want to bring them inside. As far as the sun is concerned, not too big a deal for a week or so. Don’t believe me? Go over to Lowe’s or Home Depot and see all the grapes they have inside (these are the ones they sell for like $7.99 not in a pot, but rather wrapped up in paper and soil) that simply sit on a shelf and they are exposed to artificial light and given no water and yet they are vining out nicely. So being inside won’t hurt them one bit. Now I promise to not mention that here in Dallas it was 84F and my trellised grapes are growing like crazy outside!

I would put them by a sunny window inside if that is an option ... but I agree with others they will likely be fine in the garage ...