I have a John Renwick, son of Walter Renwick and Isabel Vetch/Vietch born 1786. He had brothers Walter (b. abt 1798) and Thomas (b. 1795) and sisters Christian (b. 1790) and Margaret (b. 1793). Walter ended up in Brantford, and Thomas ended up in Michigan (Keene, Ionia Co. ) like you said. I believe Christian might have ended up in Canada as well, with Margaret staying in Scotland and marrying a Thomas Hutson. I have a letter written by Walter that would put John's death about 1835. If this all sounds right, let me know.