1. Clauses with 2 Object Pronouns
When you have two object pronouns in a clause, they will always appear in the R.I.D. order:
Reflexive, Indirect , Direct object pronouns.
I buy it (book) for myself. Me lo compro.
They sent it (magazine) to you. Te la mandaron.
Ana will give me it (money). Ana me lo dará.

2. He gives it (shirt - camisa) to me.
Él me la da.
I will write it (letter - carta) to you.
Te la escribiré.
Why won’t you tell us it (answer - repuesta)?
¿Por qué no nos la dirás?
Héctor will sing it (song - canción) for me.
Héctor me la cantará.

3. When you have a conjugated verb + an infinitive or gerund, the same rules apply as with one object pronoun. You may place both pronouns: 1) before the conjugated verb, or 2) attached to the infinitive or gerund.
I want to give it (book) to you.
Yo te lo quiero dar. OR Yo quiero dártelo.
I am giving it (book) to you.
Yo te lo estoy dando. OR Yo estoy dándotelo.
Notice, that if attached to the infinitive/gerund, you must add an accent to retain the pronunciation.

4. I am going to send you it (bill – cuenta) .
Yo te la voy a mandar. Yo voy a mandártela.
They have to sell us it (house).
Ellos tienen que vendérnosla.
Ellos nos la tienen que vender.

5. I will send him it (money). Yo se lo mandaré.
If the Indirect Object Pronoun is the 3rd person (him, her, Ud, them, Uds), where the pronoun is “le” or “les”, the Indirect Object Pronoun will change to “se” when the Direct Object Pronoun is also the 3rd person (lo, la, los, las)
We gave him it (book)
Le lo dimos → Se lo dimos
I will send him it (money). Yo se lo mandaré.
Will you give her them (magazines). ¿Se las darás?
We sold them it (car). Nosotros se lo vendimos.
Ana showed it (house) to them. Ana se la mostró.