Me, te, le

I have just started learning a little Spanish in Duolingo. Could someone explain the difference between these two sentences or is the use of either one correct:

Él le escribe un libro a Ella

And

Él escribe un libro a Ella

And the same with :

Nos comemos una naranja
And
Comemos una naranja

There's no difference between the first two examples. Spanish allows a superfluous indirect object pronoun.

There is a difference between the last two, however. The pronoun is not an indirect object pronoun. It is a reflexive pronoun. Therefore, the action of eating, when directed back on the subject, changes the action from 'eating' to 'gobbling up'.

Thanks for that. But there is still something I am not getting about the object pronouns
For example, what makes sense to me is the following

No recuerdo ellas
Mi Padre no las recuerde tambien


But from what I read the following is what I should use

No las recuerdo a ellas
Mi Padre no las recuerde tambien

It is as if I have to refer to 'them' twice - las & ellas in a single sentence. I hope this question makes sense

You can say "no recuerdo a las señoras", and you don't need any pronouns because your direct object, "las señoras" is explicit and we learn whom you're talking about.
When we already know whom you're talking about, then you can say "no las recuerdo", and that's clear enough.
However, since you're using "ellas", which is a pronoun for people, both pronouns (personal and direct object) are necessary.

- Quiero a Juan.
- Lo quiero.
- Lo quiero a él.

- Llevo a los niños a la escuela.
- Los llevo a la escuela.
- Los llevo a ellos a la escuela.

- Saludé a María.
- La saludé.
- La saludé a ella.

Thank you. That is very helpful