Thank you, Capetown,
It appears, then, that Elizabeth Greenway died shortly after the birth of Martha and Timothy took up with Elizabeth Pullum being a widower and having small children. They then had 4 more children.
I tried to join the Forest of Dean records site but it's not working at present. Can't find a marriage for E Pullum and T Etheridge so maybe they just co-habituated. Anyway, lots of work to do.
Thank you so much for your help!