Joseph & Mary Lane and descendants of TN and Robertson & McLennan Counties in TX

I am searching for information on my gggrandparents. Joseph & Mary Lane came from Tennessee into Robertson Co., TX when it was still owned by Mexico. Joseph held one of the first land grants after it became the State of Texas. Family oral history has it that Mary may have been of Cherokee descent; but, have not been able to document that. Their daughter, Mary, was my paternal ggrandmother, who married Joseph Key. Oral family history, again, has it that Joseph Key may have also been of Cherokee descent. Family history also states that he was a "circuit riding preacher." Again, no documentation, just family oral history.