Hello Trevor Mitchell. I have a Shakespeare's Birthday Book which once belonged to Surgeon/Dr Thomas Leslie Crooke 1861-1943 filled with 800-900 autographs.
Two in particular are Adam Mitchell(Crown Solicitor) and J.Fitzroy Mitchell Engineer who sadly died young in Buenos Airies. I know they once lived at "Walcott" Birr before theHoctor family took it over. I haveve other Mitchells to including a relative and great woman Poet/Writer Susan L Mitchell Dec 05 1866 (from Carrick on Shannon). I hope you may find this of interest and maybe your relatives. King regards Shane Duffy.