Hi there, I'm also working on the same line.My direct line is Elizabeth, 1805 who is sister to your Wm. 1810 (who m. Sarah Anderson) and Margaret 1807.
We lost Wm. 1810 and Margaret Allan 1807 for a while as they disappeared...(now we know to Worth Sanilac MI) because another cousin Don, found a land records where Sarah Allan had power of attorney for Wm. jr. 1810 and came up from Worth, Sanilac to sign papers of mortgage stuff.Who knew this would open up so much.
One thing has me puzzled...if George H. Allen is actually Henry, then how come on the marriage of his sister Mary to Charles Gunningham,(ref. Martha) the witnesses are George H. Allen and Henry Allen. I've now seen the orig. I guess this is a Henry from another family.??DO you know who?I also have a Robert Allen who is a witness to Margaret Allen's marriage. Again I don't know who Robert is...but I do have this AllAn Family going back to Scotland....always spelled with an A in Allan. I wrote you already at your email but maybe I got it wrong.