Hi Barb
I have the St. Andrews parish info from microfilm reels up to the mid 1850s and am slowly transcribing it into an excel file so we can all get to it on the web.
Based on what I have so far and the names you have, I found the following:
There were several Peter Grants borns in the 1790s. One was the son of Alexander and Sarah Claridge (Lancaster). The second was the son of Alexander and Marjory Murchison. The third was the son of Alexander and Hannah Grant.
There were also several John Grants. One of them matches up as a brother to Peter with father Alexander and mother Mary Murchison. There is another John Grant with father Peter and mother Christian Grant.
I couldn't find a Flora or Isabella that matched up with either of these.
Send me your email and I can send you some source files directly.

Best
Kim