My recommendation: If they are going to claim to be Christian, STOP KEEPING JEWISH LAWS WITHIN YOUR RELIGION! Otherwise, can you really be putting faith in Jesus and call the religion Christian? No, it wouldn't make it the truth.
Uh, maybe you missed the scene where Xianity grew as a sect, an offshoot of Judaism itself? Paul (who was Jewish, hence Saul) reinterpreted the Jewish faith by creating "Judaism for Gentiles", where for the first time in history you didn't actually have to be born into the "in-group". Paul took that exotic, trendy ANE religion of Judaism (think of Madonna, an ex-Roman Catholic, who adopted Kabbalism, an ancient mystical Jewish sect: same idea), but made it mainstream, widening the potential target market to anyone.
Actually, if you want to be literal (as JWs pride themelves on being), Jesus was an observant Jew until his death, and said the Torah would exist for all time; he claimed to be the messiah of Jews. He apparently never intended to replace Judaism, as it seems he believed he WAS the fulfillment of Jewish messianic prophecies in the Torah!
Sure, Xians may try to use Jesus' words of claiming to fulfill the law as an excuse to throw out all the pesky rules in the Torah (to be replaced with the Supreme Law of Jesus™: love thy YHWH with thine whole heart, and the Golden Rule that followed), but that's intentional obsfucation in order to justify detaching the OT from the NT. In essence, Xians are trying to suppress the fact that Jesus believed every last word and principle found in the OT, thus trying to make him to be kinder, gentler, than his Father.
So JWs are in a catch-22, as are all other Bible literalists: you cannot claim it's all literal truth, but then expect to be taken seriously when you start picking and choosing which elements are NOT literal truths, without looking like hypocrites.