Both players have been linked with summer exits from Spurs. The South Korean, with less than 12 months remaining on his current contract, faces an uncertain future, while has attracted strong interest from Atletico Madrid in recent months.
"Two top players. Sonny has been here for 10 years and finally got his well deserved trophy in the summer,” Frank told the media.
"Cristian Romero, World Cup winner, Copa America winner twice, very important for us. Both have trained well and set the standards. Both will play tomorrow (against Reading) and I'm very happy."
Son was appointed club captain by former head coach Ange Postecoglou, with Romero serving as one of three vice-captains alongside James Maddison and Guglielmo Vicario.
However, Frank has made it clear that he will have the final say on the captaincy for the upcoming season, regardless of whether the current leaders continue to wear the armband during pre-season.
"I haven't decided on (who the captain is) yet," he added.
"I have a long list of bullet points to get through. (Son) was captain last season and tomorrow we'll have two 45 minutes and Son and Romero will be the captains in both. I haven't decided on the captain yet."