You can do a sequential setup or parallel setup, each turbo needs to kick in at different points in the rev range or you'll have terrible lag so this requires some creating management of the wastegate.
Why not fit a larger turbo and supplement this with a supercharger creating a twincharger setup. I think this would be easier to setup than a twin turbo.
Unless your engine is heavily modified you'd probably be best off seeking a good hybrid turbo and get more boost that way, you could potentially see another 45% power gain with a different turbo and this is much easier to fit that a twin setup.
4wd conversions have been done, this is very expensive. A dimma sport car had this conversion and they used a lot of parts from a Cosworth 4x4. You'd need to do a lot of structural cutting to get this to work so it will cost a small fortune.
Why not fit a good torsen diff to the front if traction is an issue?