You are correct about the connection between the Grindells and McIntyres; however, the genealogy of the former is difficult to trace before 1861. The best I can come up with is a series of birth records to Elijah and Flora Grindell: Richard Hopewell, 1827; Tamer Ann, 1829; and Isaac, 1835. Unfortunately, I cannot connect Elijah backwards to John or forward to Clarissa Jane (b. 1836 and m. William Stewart, 1878), Adelia (b. 1854, m. John McIntyre, 1872), Richard Edward (m. Charlotte McIntyre, 1854), Susan Ann (m. Samuel McIntyre, 1851), or Tamer (m. Henry McIntyre, 1842). It is likely that they are all connected, but exactly how is anyone's guess.
Land records present a possibility. Also individual church records. I've scanned most of the latter from Queens County, so if you know the denomination of the family and what church they might have worshipped at, I can take a closer look. That's about all I can think of for the moment.