@jespah,
Nobody can, or should, be baptized without their permission and without acceptance of what it means to them.
What the LDS' are doing does not, in my opinion, hold any valididty at all and your relatives and, indeed, all Jewish people who have passed will never have any connection with them.
Probably hard to ignore by the Jewish people, but what else could be done?
Do the LDS' baptize in the name of the Father, Son & Holy Spirit? If so, I don't see how they could baptize a Jew who does not accept Jesus as the son of God.