Jonny, brother of Richie Gray, made his debut in the Premiership off the bench at half-time in Currie’s loss to Gala last week.
Fergus, brother of Edinburgh's Matt Scott, also was introduced at half-time last week and is returning from a shoulder injury.
James Johnstone continues at centre for Currie while Sean Kennedy is back with County after making his Glasgow debut against Zebre last weekend.
George Hunter starts at prop for league leaders Ayr as they travel to take on Edinburgh Accies. Nick Campbell is on the bench for the Millbrae men.
Taylor Paris is on the wing for Dundee HSFP as they host Gala while Fraser Thomson and Bruce Dick play for Melrose against Boroughmuir.
Scott Wight is in the extended Aberdeen squad named for the trip to play Heriot's at Goldenacre.