This may or may not be the Frank and Mary(altho I have it down as Marion) Jensen Nelson you are looking for but: Our gggrandfather's(Alonzo Bates from Waupaca County) grandson William Bates married an Anna Amelia Nelson -listed on marriage license as daughter of Frank and Marion Jensen Nelson. Anna was born April 27th, 1889 and died June 4th, 1914 in Saxeville, WI.(Waushara County) They were married May 18th, 1908.They had 2 children that we know of for sure- Guy and Leona-she died as an infant and Guy died around the age of 19. I don't have any info on her brothers or sisters tho-but never really looked too hard either. Seems like a pretty good coincidence that Anna was your grandfather's sister???