If you are looking for Thomas' parents he could be the Thomas Kilgour who is listed in the 1851 and 1861 Scotland census as the son of Peter and Jane of Perthshire County.
His death certificate and obituary may have the parents' names. His obit may have surviving siblings especially any that might have immigrated.
The 1900 census shows he immigrated in 1873 and was a naturalized citizen. He probably filed for citizenship at the Clarion County Prothonotary Office. Listed on the State of Pennsylvania manifest, which landed in New YorkMay 9, 1874, was a Thomas Kilgour 23.
The 1900 census also shows Charlotte had 12 of 13 surviving children. One you left off was also named Charlotte.
Check with the Clarion County Historical Society and Eccles-Lesher Memorial Library in Rimersburg to see if they can help you. They should have cemetery, church, newspaper and other records that might be of help.