Dual imaging is feasible and it does work - but it is a real pain. I tried it to beat the weather - tried imaging mono & colour at the same time. Biggest problem is flexure and with 2 DSLR's I don't think you will overcome it. My setup -
http://www.pbase.com/loc46south/image/120564600
It used a ED120 Equinox and a SW100EDPro on a Losmandy double saddle Plate. I used internal guidence for mono Luminance and external guide head for narrowband. The ED100 shot continuous colour and I ended up using an AO8 to get rid of flexure issues between the two scopes.
The biggest problem comes when you want to automate it and use off star auto focusing - fun fun fun
. In the end I gave up and bought a M250.
Geof