The two feats Saving Shield And Bodyguard allow you to grant bonuses to adjacent allies who are being attacked. If a character with both feats is defending an adjacent ally would both feats apply? One uses an immediate action and the other uses An attack of opportunity action.
At the expense of an immediate action and an AoO, you can grant your Ally +4 to his AC for one attack. Note that Saving Shield will last for the entire attack or full attack, Bodyguard only for one attack, though you can use it multiple times a round.
Bodyguard grants a +2 shield bonus, which does not stack with any other shield bonuses your ally might have.
Aid Another grants
Since no type is specified, it is an untyped bonus. These generally stack with all other bonus types.
You can use one or both or none, depending on action economy, location of opponent, and your current status/condition.
If the opponent who is attacking is outside your threatened range, you can not use Aid Another, thus Bodyguard is not usable.
If you are flat-footed, unless you have an additional feat such as Combat Reflexes or a class feature like Uncanny Dodge, you can not do either.
Otherwise the shield bonus and untyped bonus will stack giving a +4 to your ally's AC.