Would the Broncos really defend their Super Bowl title in 2016 with a group of quarterbacks consisting of Mark Sanchez, Trevor Siemian and a rookie?

They appear to be answering that question by continuing to explore a trade for 49ers quarterback Colin Kaepernick, who met with Broncos general manager John Elway at Elway’s house in the Denver area Thursday, a source said. Kaepernick and Elway have met at least twice since March 15. Kaepernick has spent his offseason rehabbing three injuries in Vail, Colo., which is about 100 miles from Denver.

Their meeting Thursday occurred on the same day that Kaepernick’s $11.9 million base salary became guaranteed, a development that erased the unlikely possibility the 49ers would release him. The 49ers have granted Kaepernick’s agents permission to seek a trade. In doing so, the 49ers have allowed any team interested in Kaepernick to speak with him directly. Without that permission, teams can’t approach players under contract to another team.

Sanchez, 29, and Siemian, a 2015 seventh-round pick who barely played as a rookie, are the only quarterbacks on Denver’s roster. Last month, Elway said the Broncos weren’t done addressing the position after trading a conditional late-round pick to the Philadelphia Eagles for Sanchez, who has the lowest passer rating (74.3) among the 24 quarterbacks with 2,000 pass attempts since 2009.

The Broncos have the 31st overall pick in the upcoming draft, which means they are unlikely to land one of the top quarterback prospects in Carson Wentz, Jared Goff or Paxton Lynch.

The Broncos have been working on restructuring Kaepernick’s contract, which calls for him to earn a total of $14.3 million in 2016. The Broncos, who have just $1.62 million in salary cap space, would need to clear salary cap room before a potential trade for Kaepernick could be completed.

Denver could clear significant space by trading or releasing left tackle Ryan Clady, who is scheduled to earn a $9.5 million base salary this season. Clady, 29, is a four-time Pro Bowler, but he has missed 30 games over the past three seasons. He didn’t play in 2015 because of a torn ACL and became expendable after the Broncos signed Seahawks left tackle Russell Okung in March.

The Broncos have reportedly placed a fourth-round value on Kaepernick, but they don’t have a fourth-round pick this season. It’s not known whether the 49ers are interested in receiving Clady as part of a trade for Kaepernick.

The 49ers have left tackle Joe Staley, 31, a five-time Pro Bowler, but a question mark at right tackle. Anthony Davis has said repeatedly on social media that he will return this season after taking a one-year sabbatical in 2015 to address health issues.

In late February, ESPN reported that Davis was formally set to apply for reinstatement. On Friday, however, the right tackle said, via Twitter, that he will apply for reinstatement “later this year,” adding that dealing with general manager Trent Baalke was giving him a headache.

Given that, it’s unlikely Davis will be present Monday when the 49ers begin their offseason program.

It’s not known whether Kaepernick will be medically cleared to participate in the start of the offseason program. He has undergone surgeries to his shoulder, thumb and knee since late November.

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch