Real-estate lawyer Ms Carson and Mr Carruthers, a specialist in contentions planning litigation, join Morton Fraser as partners on June 2.
The pair previously worked for Scottish law firm Semple Fraser until it collapsed when they joined Dundas & Wilson in March 2013.
Dundas & Wilson and London-based CMS merged at the beginning of this month.
The pair will be joined by senior associates David Stewart and Mark Colquhoun and senior solicitor Ursula Currie.
Morton Fraser chief executive Chris Harte said: "Elspeth and Ken are both recognised as leading individuals in their respective fields and are great additions to our highly regarded real estate and planning practices."