Joint practices are a regular feature of typical training camps, but there has been little discussion of them as the NFL schedule remains in a state of uncertainty due to the coronavirus pandemic.
The Falcons are slated to play the Dolphins in Week 1 of the preseason and the Bills in Week 2. Assuming the preseason schedule goes ahead—a big if given that most states are in the infancy of re-opening—the teams could hold practices before their games.
It will nevertheless be a play-it-by-ear situation, especially in regard to safety and travel. The NFL, perhaps more than any other league, is incapable of having a centralized location for its games. The only way the league will be able to operate is if most teams can play in their home stadiums, even if those matchups are held without fans.
Ideas like joint practices are in the theoretical stage right now.