Hi, like many of you, i have a T2 for filming weddings.
But how can i use it with a stabiliser, 30 cm movement brings everything out of focus?
What lens do i need for walking around with a stabiliser, and maintaining nice bokeh when shooting standing still? Or do i need to change lenses all of the time?

There are three things that affect depth of field: focal length of the lens, f-stop, and subject distance. A wider lens will have more depth of field, a higher f-stop (smaller aperture) will have more depth of field, and a subject that is farther away will have more depth of field around it. To maintain focus while on a stabilizer, you either need more light, a wider lens, to stay farther away, or have someone pulling focus remotely.

Using a wide-angle lens is the best way to fix this problem. Apart from giving you a deeper DOF, WA will also make your steadycam work look a lot better as the wider angle will make any bumps or wobbles look less noticable (not that I think you don't know what you're doing with a steadycam; it's just that at weddings you need every bit of help you can get!)

Something like the Tokina 11-16mm f/2.8 or the Sigma 10-20mm f/3.5 will work great.

If you use Magic Lantern, you can also look at the lens data to help plan your shots. You can quickly and accurately check out where your DOF near and far points are and work out how far away you need to be to keep everything on in focus. This a great feature of ML and I use it regularly when setting up steadycam shots.