John, I really thought I'd explained exactly what has happened here but you don't appear to be grasping it.
As confirmed by you, 'your' Thomas Brown married Annie Barrett in 1921.
I already gave you his RC baptism details in 1899 at Our Lady of St. Carmel, Liverpool stating his mmn was Owens (as was his birth entry), also that of his sister Rosa Anna (we know from census she was his sister) born in 1901 (her birth entry shows mmn Edwards but her baptism shows Owens, like Thomas'.
Thomas' 1899 baptism entry (you can view on Ancestry) has been added to by a priest stating he married Annie Barrett in 1921.
There are not 2 John Browns, Dock Labourers, with wives named Alice, in Toxteth/Liverpool - only your couple and their family which includes Thomas and Rose Ann.
All their children births show mmn Edwards EXCEPT for Thomas showing mmn Owens for some reason, plus when Rose Ann (Rosa Anna) baptised 2 years later her mmn is given as Owens.
As I stated before, I can't explain why mmn was given on both Thomas birth entry and baptism as Owens, and on Rose Ann's baptism also given as Owens (when her birth entry is Edwards). I would suggest looking further in Alice Maude Edwards background - the name Owens must figure there somewhere for it to have been used with 2 of their children.
I really don't know what else I can say or do to make you understand especially having given you his RC baptism where a priest has noted that he married Annie Barrett 1921.
Annette