Not sure about remixes but you are allowed to do covers because you are protected by PPL since you own the performance rights (as long as you recorded everything yourself). YouTube has a system in place where you can revenue share with the rights owners (publishing companies, record companies and the composer), who obviously owns the composition and original recording rights. I recommend looking at and learning as much as you can about PRS and PPL (also, join them as well as the musicians union) as they're the two main companies to support both performers and writers of music. Also, going through all of YouTubes music covers policies may help since there might be some stuff about remixes in there.