The baptisms for East Brent are all on FreeReg.
Matilda Pyke was baptised there on 30 May 1822, and again a couple of weeks later, daughter of John and Elizabeth. She had a sister Caroline, born 1820, who was the mother of Sylvester, born 1837.
Sylvester (shown as Pipe) was living with Sidney and Matilda in 1851. He's shown as a lodger, but would have been her nephew.
There's a death registration for Matilda Poole in Axbridge district in 1864, shown as age 45, so a couple of years out, but I still think this might be your Matilda. Maybe she was never married to Joseph Bunley.
Sidney Poole died in Axbridge district in 1854, age shown as 34.
Again using FreeReg, Sydney Poole was baptised in Huntspill on 4 February 1821, son of Thomas and Frances. So the age at death fits in with this baptism.