When you set your lens at infinity, depending on the lens, will your shots all be in focus so long as the subject(s) are a certain distance from the camera? I wonder how that distance is measure?
3 lens: Sigma 30 1.4, Tokina 11-16 2.8 and Canon 17-55 2.8.

I want to setup my camera in small makeshift studio by myself (Not help from the wife wanted) to make some video Christmas cards.

your markings are on the lens. If you look at the reading when you are zooming it will tell you how far the subject has to be from the lens. To be precise you can pull out the tape measure and be exact.

It sounds like you looking for the Hyperfocal Distance for your lenses. This is the focus setting that will provide good focus from infinity to half the selected fousing distance. The Hyperfocal Distance depends on three things: The focal length of the lens, the aperture (f-stop), and your definintion of "good" focus. Here is a chart that you can use to calculate this.

Hyperfocal Distance Chart - DOFMaster (http://www.dofmaster.com/charts.html)

You will see that for wide apertures (low f-numbers), the distances are rather long, so I don't think it will be relevant for your studio (unless you have a really big studio), but for short lenses and high f-stops,it may be useful for finding the greatest depth-of-field.

As you can see, and to answer your question directly, there is a distance where everything behing it will be in focus, but it's not infinity, it's one-half the hyperfocal distance for the particular lens and settings you are using.