The solution is to have the original actor play Short Round. He and Indy do the grumpy old men/odd couple thing while their sons actually do the action hero stuff.

Something happens to Mutt and Indy goes to Short Round for help rescuing him. He says he's too old to help, but sends his son (Steven Yuen, named Indiana by Short Round). The first act ends with Mutt being rescued/found and the fathers being simultaneously kidnapped.

The second act is the old dads and the young sons in parallel stories running for their lives and bonding while assuming the other pair is back safe loafing around.

The third act is them meeting up and resolving the plot, with Indy and Short Round settling up/recconnecting, and Mutt and Short Round's kid deciding to team up.

Indiana Huang and Mutt Jones.