Karen, I realise this message is very old, hope you are still looking for information re siblings of Margaret DOLLEY.
My 3G grandmother was Caroline DOLLEY, baptised 20 JUL 1800 Wimbledon, Surrey, England Father Thomas DOLLY, mother MARY
She married my 3G grandfather George HYDE 19 Jun 1828, Saint Bride, Fleet Street, London.
According to IGI, there were several other children born to Thomas and Mary.
Baptism of children, Wimbledon, Surrey, father Thomas Dolly, mother Mary Caroline Dolly, 20 Jul 1800 Melancthon Dolly 20 May 1802, Thomas Dolly, 3 Feb 1805 Margaret Dolly, 13 Nov 1806 William Dolly, 27 Jan 1810 Mary Dolly, 27 Jan 1810 Batch P013441
I have traced Caroline, Melancthon and Thomas through the censuses, no trace found so far of William and Mary.