Play 2nd DLC without 1st
On the Ubisoft Offical Store, the description of DLC 2 reads:
This is extra content for a game which need the game to run.
There is no mention of needing another DLC in order to buy and use this one. The same sentence is present on the page of DLC 1.
In those descriptions, there is no detail about what are the level caps and new abilities introduced by the expansions, as when they were published on the shop, this information wasn't avalaible to players.
So according to all this information, I think you can play DLC 2 without owning DLC 1.