Scotland call up Conway and Mackay-Steven
However, Celtic's James Forrest and Birmingham City's Chris Burke have been forced to withdraw through injury.
Dundee United's Mackay-Steven has yet to make his full international debut, despite being included in several squads under new boss Gordon Strachan.
Conway, meanwhile, has found form since moving on loan to Brighton and Hove Albion from Premier League Cardiff City in September, having won the last of his five caps as a substitute in the 3-2 friendly defeat against England at Wembley in August.
Both will now hope to get a chance to shine in the upcoming double-header, which sees the Scots face the United States at Hampden Park on Friday before taking on Norway in Molde next Tuesday.
Forrest has dropped out of Strachan's group after being withdrawn in the 71st minute of his club's 4-1 Scottish Premiership win over Ross County on Saturday, while Burke was forced off in Birmingham's 3-1 win at Huddersfield Town.