Should I tell my referees that my application got rejected ? (I intend to re-apply)
I think the answer may depend on the exact relationship you have with your referees. I would think that if they were willing to write you a reference letter in the first place, they are invested in you and your academic success enough to warrant an update on your graduate admissions status. I think if you just emailed them for a new letter, they may wonder why you're requesting more letters relatively late in the application cycle, or they may ask about the status of your past applications. In either case, it is likely that you will need to disclose your rejection, so perhaps disclosing it first is a better strategy.

Plus, this may be a good opportunity to solicit feedback from them on your past application so you can incorporate any feedback given into your April application.