1.) Yes. See
http://bytemaster.bitshares.org/update/2015/01/08/DevShares-Reloaded/a.)
Download the DevShares client, install and import your private bts key to the DevShares client to claim your balance.
b.) No. Your BTS balance at the time of the snapshot determines the amount of DevShares you receive. Beyond that, it has no effect on your BTS balance.
c.) I've read that there could be some risk involved with importing your BTS private key to a new DAC client, because of possible exposure of your private keys. (That's the reason that a dev created a method to import without using your private keys for PTS DPOS). Importing your private keys to the new client is also the standard practice for claiming shares -- so I don't know about the level of accepted risk we're taking. Other than that, it will have all the risks inherent in a live testing environment, so whether it's worth playing around with the shares that have been given to you depends on how you're defining risk.
2.)
According to the recent newsletter Sparkle had a snapshot on December 14th, 2014 and will honor AGS, PTS, and BTS with 33% each.
a.) You claim them the same as 1a.) once Sparkle is launched, which is also covered in the recent newsletter above and will not be until the BitShares 1.0 client is released.
b.) Claiming shares that have been allocated to you based on your BTS holdings will not affect your BTS balance.
--- The concept of sharedropping is that you are 'targeting' the gift of an initial percentage of shares to a demographic that, by then becoming shareholders, will be most likely to increase the value of the new DAC. This would not be effective if you were forcibly taking something (like your BTS shares) from them at the same time ---