Amberly,
There's a marriage that may be worth considering, again at Tarvin, 25 APR 1773 Thomas Betwizel to Rachel Firat/Sirat.
There's also baptisms for 2 more children to this couple. I wonder if the name has corrupted over several generations, as it appears that neither the bride or groom could sign their names. My thoughts that Betwizel, could have been the more familiar Birtwisle, well known in Cheshire, and I believe could quite easily have been corrupted into Boswell - but that's for you to ponder.