Actually the falmer were forced into their situation as the ancient nords waged a genocide against the elves that Forced them into their situation then they were stuck in the sad case of betrayal by the very elves thought were their friends.
I don't know why you're bolding "forced' as if it carries some hidden meaning, but I'll respond anyway.
They're trying to block out the sun which will "force" everything else to live in darkness, and survive in dark dank caves, and may eventually become like the Falmer.
That's assuming the food inside caves aren't lethal to them. And if they are then the people will be forced into cannibalism to survive. Maybe eating each other, maybe turning the tables, and eating vampires. Who knows?
Only one things for certain. Everything will go to [censored].
It really should be pointed out that vampirism in Skyrim is actually quite harmless. If you are a vampire no one will die or be turned if you feed on them.
No. In Oblivion one of the ways to become a vampire is to let a vamp feed on you in your sleep.