1. We are going to tell John what happened.
John= indirect object correct
2. Are you going to explain to your parents why you arrived home late? (Is this sentence grammatically correct? yes)
Parents=indirect object incorrect
3. She isn't going to call us tonight.
Us=direct object correct
4. I love my mom a lot.
Mom=direct object correct
5. They aren't going to lend her the money.
Her= indirect object correct
6. You never tell me the truth.
Me=indirect object correct
7. Are you going to write to your relatives?
Relatives= indirect object incorrect
8. She doesn't hate them.
Them= direct object correct
9. I always do them(homework).
Them=direct object This sentence doesn't make sense.
10. Are you going to invite her to the party?
Her=direct object correct
11. I am not going to tell her the truth.
Her=indirect object correct
12. I am not going to explain anything about what happened to them.
Them=indirect object incorrect
Indirect objects in English do NOT have the preposition "to" or "for" in front of them.