What should my next step be?

[IgorStrav]

You can use the GRO website
https://www.gro.gov.uk
to search births and deaths free of charge (you do have to register).

I looked for the name you quoted and the result is as shown....

[IgorStrav]

William and Louisa Jane married in the October quarter of 1903 in

Freebridge Lynn reg district.
County:   Norfolk
Volume:   4b
Page:   869

As expected, William Allison and Louisa Jane Cooper

I got these results from Ancestry, but you can also find them on free sites such as Free BMD

[IgorStrav]

I can see William through the censuses in Gunby and Wormegay (great name!) in 1881/1891/1901 with his parents George and Mary Ann, and then with widowed father George in the 1901.

Just looking to see if I can find George and Mary Ann's marriage.

[Ladyhawk]

Was just about to post marriage entry detail along with birth entry

ALLISON, EVA  LILIAN   mmn COOPER
1909  D Quarter in DOWNHAM  Volume 04B  Page 290   

ALLISON, THOMAS   mmn COOPER
1906  J Quarter in DOWNHAM  Volume 04B  Page 320   

Eva Lillian   Allison
Year   1931
Polling district or place   Sheringham
Constituency   P C of Norfolk, Northern Division
Constituency in full   Parliamentary County of Norfolk, Northern Division
County   Norfolk
Address Links Way Links Road

[IgorStrav]

I believe this is the marriage for your grandmother's grandparents - your greatx2 grandparents

George Allison
Reg Year:   1864
Quarter:   Jan-Feb-Mar
Reg district:   Spilsby
County:   Lincolnshire
Volume:   7a
Page:   761

with Mary Ann Clark

And this is your great grandfather William's birth

ALLISON, WILLIAM       MMN CLARK 
GRO Reference: 1877  D Quarter in SPILSBY  Volume 07A  Page 617

[ayahuasca]

This is amazing! Can’t express what it means, I appreciate it so much. Can’t wait to correct the tree and see what happens!

[Ladyhawk]

This looks to be Louisa Jane Cooper’s baptism

Louisa Jane Cooper
Baptism 07 May 1882
Residence   Norwich
Father   John
Mother Easter Hines

COOPER, LOUISA  JANE   mmn HINES
1882  J Quarter in FREEBRIDGE LYNN  Volume 04B  Page 321   

and on the census with her parents

1891 RG12; Piece: 1564; Folio: 70; Page: 9

Thatched Cottage, Lynn Road, Hillington, Freebridge Lynn, Norfolk
John   Cooper   Head   Marr. 1847   Agricultural Laborer   Norfolk
Esther   Cooper   Wife   1857      Norfolk
Ernest   Cooper   Son.   1878   Agricultural Laborer   Norfolk
Henry   Cooper   Son     1880   Agricultural Laborer   Norfolk
Louisa   Cooper   Daugh 1882   Scholar   Hillingdon Norfolk
Edward   Cooper   Son      1891   Norfolk
Charley   Cooper   Son       1885   Scholar   Norfolk

Marriage entry

Dec 1876   
COOPER.    John        Freebridge L.    4b   918    
HINES    Esther        Freebridge L.    4b   918

[Raybistre]

There is a record of a Lilian Allison marrying in Forehoe Registration District in Norfolk in Dec quarter 1934. Possible spouse listed as George Newell. Ref 4b 543.
Ray

[IgorStrav]

And then the 1939 shows Lilian E Newell born 3/11/09 with a younger male also named Newell born 29/8/32.  There's a green annotation above the first name and initial of this male, suggesting (I think) that the names should be reversed.

The dob obviously predates the marriage, and there's a birth ref under Lilian's maiden name for this male in Oct quarter 1932, at St Faith's Norfolk.  This birth ref confirms the green notation reversing the first names.

I think ayahuasca already had this info.