3 and one more, Mary Jane Gavin Lodge born 1909 (mother's maiden name of Gavin), also in Port Glasgow.
Mary Jane Gavin Lodge married in 1929 Port Glasgow to John McGhee, which was why I don't think she is a possible mother to Thomas born 1930
Have looked further into the family and this Mary Jane Lodge born 1909 was half-sister to your Mary McAllister Lodge.
Children of Thomas Lodge and Catherine/ Kate McNeill (married 1898):
Maggie 1895 (born before marriage - daughter of Catherine?)
Elizabeth Lodge 1898
Thomas Lodge 1900
Mary McAllister Lodge born Dec 1902 Port Glasgow
Catherine Lodge (nee McNeill) died 1906 Port Glasgow. ** (see added below)
Once you have her marriage certificate you will get her parents' names. This should lead to her parents' Scottish death certificates, to census records, and possibly to Irish records. (If we can help - just ask.)
Thomas Lodge
2nd marriage 1909 Port Glasgow to Bridget GIRVAN
1911 census Port Glasgow - Lodge family
Thomas Lodge 36
Bridget Lodge 31 (2nd wife)
Lizabeth Lodge 13 (child of Catherine McNeill)
Mary Lodge 8 (child of Catherine McNeill)
Mary Jane Lodge 2 (child of Bridget Girvan)
Patrick Lodge 0 child of Bridget Girvan)
Lodge Family - 1921 census Port Glasgow ref 574/ 14/ 26 Thomas Lodge 48
Bridget Lodge 43
Mary Lodge 18
Jane Lodge (Mary Jane) 12
Patrick Lodge 10
David Lodge 8
**ADDEDOn her death 1906 - Catherines Lodges mother maiden name shows as McIlheron.
Possible death-
Catherine McIherin / McNeill / Cameron died in Gourock in 1911, age 69 (so if the informant has remembered correctly, she had 2 marriages to Cameron and to McNeill). Her mothers maiden name was Blaney