Just found Thomas (son) on the 1881 Census.
He was living at 7 Cromwell Terrace with his Auntie Elizabeth (Price) and husband William Porter again. There's a Jane Mercer, niece, aged 17, b. C. 1864, living with them too. I have no idea who's her, and looking at the GRO, b. 1864 +/- 2 years, there are two:
MERCER, JANE DAWSON (DAWSON)
GRO Reference: 1864 S Quarter in WEST DERBY AND TOXTETH PARK Volume 08B Page 297
MERCER, JANE VICTORIA PRITCHARD FOX (CARNEY)
GRO Reference: 1864 J Quarter in WEST DERBY AND TOXTETH PARK Volume 08B Page 349