Vit A is the vitamin to support mucosal tissues. You can get a high qty of vit A in cod liver oil. You can take it directly and also give some to him.
Coconut oil fights fungal infections. raw virgin coconut oil can be taken by the teaspoonful directly into the mouth of you and the infant. No harm. In fact they put coconut oil in formula.
Sage oil is a broad spectrum antibiotic useful for bacterial sinusitis but i cannot suggest it direct to an infant.