Are they tweeters? If I replace them, do I need to install crossover? Anyone replaced them and how difficult is it? I replaced the HU and 4 speakers on the door already.

 

Yes they're tweeters. Can't answer any replacement questions, but yeah I think you'll need to put crossovers in to make use of the new tweeters you're planning to swap in.

 

you don't need to install components to make it work... you can rig up co-axes to work if you know what you're doing but for the price diference you may as well run a proper component... even if you go with the stock tweeter