According to the 1901 Census Transcription for Scotland on Find My Past, this is the only entry for a Martin KENNY born 1899 +/-5 years:
Address: 56 Cuthbert Street, Bothwell, Lanarkshire, Scotland
Martin KENNY, head, married, male, age 38, Coal Miner Brusher, born Ireland
Mary KENNY, wife, married, female, age 35, born Ireland
John KENNY, son, male, age 14, Scholar, born Bothwell, Lanarkshire, Scotland
Kate KENNY, daughter, female, age 5, Scholar, born Bothwell, Lanarkshire, Scotland
Martin KENNY, son, male, age 1, born Bothwell, Lanarkshire, Scotland
You can view the original entry for a fee at https://www.scotlandspeople.gov.uk
I note that your sources for Martin Kenny b. 1899 include his birth certificate. This should give further details on his parents & the date they married.
Note you can now complete FREE searches on ScotlandsPeople, but there is a fee to view the actual certificate/record.
In the 1911 Census (at Scotlands People) there is this family:
Registration District: Cowdenbeath / County: Fife / Ref. 410/1 11/27
Mary KENNY, age 49
John KENNY, age 24
Catherine KENNY, age 15
Martin KENNY, age 12