|No you cannot run two routers in parallel on one DSL line.|
One presumes the 2wire device is actually a modem/router combo unit since you must have a modem in order to connect to internet.
How long a distance between buildings?
You may be better off with exterior directional antennae to boost the wireless signal strength as long as you have direct line of sight. Either that or run a Cat5 cable beside the phone line provided the cable length is less than 100m.
Goin' Fishin' (Some day)