Hi Jack, It's been awhile since I checked on my Sangster Line. John and Isabella had at least 2 children: Isabella Mehitabel b. 21 Jun 1805 and Michael b. 07 Oct. 1807. I don't have anymore info on them. After Joseph died in 1775 Margaret Mann married Edward Kergan(Carrogan) Oct 26 1786 and they had 2 children: Margaret b. 1797 d. 18 Jan.1872 married Rufus Whitman 02 Feb 1813 and Catherine Born or died(I don't have that info) married Michael Flynn 28 Mar 1815.
That is all the info I have on them. Hope this helps you.