I agree that it looks unlikely that Robert and Jane married.
Nathaniel and Elizabeth appear to have had at least 7 children:
Sarah bp.21/6/1789 St. Lukes, Chelsea
Elizabeth bp.4/4/1791 St. Paul, Covent Garden, Westminster
Lucy b.15/4/1793, bp.5/5/1793 St. James, Westminster
Nathaniel George b.23/1/1796, bp.3/3/1796 ditto
Jane b.28/1/1798, bp.25/3/1798 ditto
Charlotte Elizabeth b.5/7/1801, bp.13/7/1801 ditto
Robert Jasper b.3/1/1806, bp.20/1/1806 ditto
Annette