1) A dual 4ohm sub can be wired in series giving a 8ohm load or in parallel giving a 2ohm load.
Now if the amp is bridged that means the amp is seeing half the ohm load meaning if it is bridged at 4ohms the amp is seeing 2ohm. (look at spec sheets for an amp and you will see them rated at say 4ohm mono and 2ohm stereo as lowest possible impedences, this is why).
2)Yes a DVC speaker can be wired to two identical bridged channels or two identical amplifiers. Either way, the channels just have to be carefully gain matched.
3)You can bridge your 4ch amp to a single DVC speaker. The two bridged channels just need to be gain matched. I would however just sell it and get a nice 2ch or mono amp though.
2008 Mazda CX-7 GT
Kenwood DNX9140, Rockford Fosgate T600-4 T1000-1bd, Dayton RS225 8's, Energy 3.5, OZ Matrix Elite 15.2
"Your sister is hot but your mom does that thing with her tongue..."