I have some information that may mesh with yours. I want to be clear, this is simply some information that came from family sources. I have not made it to these people to verify the data and to secure sources...however, just about all of the info I received from these sources have proven to be accurate. Some members of the Huffman family have maintained a loosely compiled family history for generations, and this info comes from that as a source. They did tend to do a straight lineage rather than a good family cluster, however.
I have a Michael Hufman (note spelling - his child used the double f we use today) with no birth date. I have a death date of 1803 in Harrison County, KY.
All I have for his spouse is a first name. Catherine.
I have as his parents: Father: Johann Wilhelm Hofmann (again...note spelling). Mother: Agnus.
Michael's son (if this is the same Michael...this would be your Rachel's brother): Anthony Jacob Huffman...born in 1770 in Augusta County, Virginia. Died in 1846 in Newell Township, Vermillion Cty, Illinois (which is where my Huffman lineage is largely concentrated). Anthony is my 4th great grandfather.
It is not much, but perhaps they are clues for you. Regarding Michael...we do not have all of his children, so I am not sure if he had a daughter named Rachel.
Feel free to contact me about this. It would be great to collaborate on this part of the family.