It wouldn't matter whether it made me worse than them, although I would like to hear why you would think so. This kind of personal revenge isn't about what is right or seeking justice, it is about punishing and killing the SOB who took away my sole reason for living. Because if someone took my wife and son intentionally and with malice then regardless of the moral position of such an act i would replace my wife and son as my sole reason for living with the singleminded and implacable intention to hunt down and personally punish those responsible, no matter how long or how hard it was.
Any kind of humanity or morality I may currently possess would simply be removed, replaced with that implacable intent to make them pay, and pay in the worst imaginable way I could possibly countenance.
I understand that is wrong, both morally and legally, I understand that it will not bring closure, I understand that it will never bring them back, I understand that in doing so I would almost certainly pay the ultimate price myself or at least lose my own humanity.
The point to remember is, I wouldn't care. I would only care about retribution. My life would be entirely about enacting that retribution.