The drawing shows a through tenon and a blind tenon that meet (or nearly so) inside a leg.
Questions:
How deep is deep enough to make a mortise and tenon joint useful?
Are there other strategies to deal with this situation?
Would you make a blind tenon that was smaller in the vertical dimension, allowing it to go deeper, through the other tenon?
Would you bother making the blind mortise and tenon joint at all, or might you choose some other kind of joint, since it won't show?