I think I may have some more information for you. Whilst looking for my family I have found a John Tonks in Gloucester in 1891. He was married to a Sarah BUT she was born in Staffordshire and NOT Bristol !!! They have children but not Blanche.
I thought it somewhat odd that Blanche was born the same year that Caroline died. !!! Where did you establish that John married Sarah Bate?
I also believe that John and Walter could be brothers (1881 census).