For the last few decades Superboy has been a teenage clone of Superman (and I think it turned out Led Luthors DNA was added in making him a human kryptonian hybrid... comics are weird). Supergirl was Superman's kryptonian cousin until she died and the DC continuity was rebooted. Then Supergirl was a shapeshifter that took up the mantle. Then Superman's cousin was reintroduced. And of course this whole time there was Power Girl who was Superman's cousin from a parallel universe running around too.

As far as I know Superwoman is basically a female version of Superman from yet another parallel universe but I could be wrong.

And that's the overly simplified version of events that hasn't really applied since New 52 rebooted everything again. As convoluted as comics can get, DC is the absolute worst.