I think some of my relatives and ancestors will be turning in their graves at the thought of being baptised into the LDS church or for that matter any church. My objection is that the person being baptised has no say in the matter, but then I suppose these feelings are left overs from my family's baptist background of adult baptism.
You seem to totally misunderstand the proxy baptisms carried out by the LDS.
Part of the beliefs of the LDS is "life" continues after death of the physical body.
They believe that the dead are capable of making the rational decision of accepting or rejecting the proxy baptism offered on their behalf.
If the LDS are correct in their beliefs then your ancestors are in the best place to make an informed decision on the subject.
If the LDS (and other faiths) are wrong and there is no "life" after death then it makes no difference.
Cheers
Guy