In your example, those are just two different meanings. For example "Nous avons parlé de foot à mon fils" means "We talked about soccer to my son". As you can see they have different functions and can be used in combination. Nothing to memorize here, you just need to understand the function of the preposition.
For the verb "aider" I can not find an example using both that is commonly said. "J'ai reçu l'aide de mon père à porter mes valises", is not usual (maybe even wrong). "J'ai reçu l'aide de mon père pour porter mes valises" or "Mon père m'a aidé à porter mes valises" are both correct. The first translates to "I got help from my father to carry my luggages", while the second translates to "My father helped me to carry my luggages".
You can also use it for directions like "il y a moins de deux heures de route de Cannes à Marseille."