Louis was a Brass caster and worked alongside his brother Albert at Bayliss' in Birmingham

Elsie can be seen as a child of 5 years in the 1901 census, born in Moseley, Worcestershire, living with her parents Alfred and Ellen and 6 siblings. I assume Ann Mortiboys was the head of the household, and that Alfred was perhaps her younger broteher and lived with her at the time.
Ann Mortiboys 53 Staffs Potteries Worcester    
William Mortiboys 21 Warwick Nechells Worcester Cycle Rim Polisher
Emma Mortiboys 19 Warwick Nechells Worcester Cartridge Tester
Alice Mortiboys 17 Warwick Nechells Worcester Bullet Filling Lead Gds
Ada Mortiboys 13 Warwick Nechells Worcester 
George Mortiboys 6 Warwick Nechells Worcester    
Alfred Mortiboys 41 Warwick B Ham Worcester Bricklayer
Ellen Mortiboys 40 Worcester King's Heath Worcester    
Jessie Mortiboys 15 Worcester King's Heath Worcester    
Oswald Mortiboys 11 Worcester King's Heath Worcester    
Stephen Mortiboys 10 Worcester King's Heath Worcester    
Frank Mortiboys 7 Worcester King's Heath Worcester    
Elsie Mortiboys 5 Worcester Moseley Worcester    
Hilda Mortiboys 2 Worcester Kings Heath Worcester    
Harold Mortiboys 11 Months Worcester Kings Heath Worcester    

In Memory of
Private LOUIS RONALD KNIBBS

7348054, Royal Army Medical Corps
who died on 31 May 1940
Private KNIBBS, Son of Louis Percy Sydney and Elsie May Knibbs, of Stirchley, Birmingham.

Remembered with honour
BIRMINGHAM (BRANDWOOD END) CEMETERY


Whilst the CWGC web site doesn't provide details of where Louis died, there were Military hospitals at Birmingham during the Second World War, including No 7 Canadian Hospital at Marston Green. Birmingham and Coventry were among the chief manufacturing areas producing materials for the war effort and were therefore subjected to many devastating air raids during the Blitz of 1940-41. It is quite likely that Louis died in one of those air raids.