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Always thanks for your answers. I posted this question a couple of days ago, but nobody has answered. I am hoping somebody help me again.

Let's imagine a situation.

My parents are scheduled to come back from their trip tomorrow.
My younger sister did something wrong, and I think she should confess her fault to her parents as soon as/when they come back.
But she is determined to hide it from them.
I am going to advise her to confess.

No.1
"If I was/were you, I would confess my fault to them as soon as/when they would come/will come/come/came(?) back"

No.2
"If I was/were you, I would confess to them that I did something wrong as soon as/when they would come/will come/come/came(?) back"

No1 may be simpler and easier to understand, but I would like to point out No2.
As you can see, There are two more subordinate clauses In No.2
One is That clause, and the other is as soon as/when clause.

In no.2, I didn't used "would" in "that clause" with an idea it's unnecessary to use "Would" because I was going to report "a fact" that I did something wrong.

Here is my question.
It's clear and undeniable that my parents come back tomorrow.
Even In this situation, should we use "Would" or "the past form" to express something theoretical?
or use "will" or "the present tense form" because it's clear for my parents to come back tomorrow?
Between the four choices, what should I pick up? I am in need of your answers. Thanks for reading.
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"If I were you, I would confess to them that I did something wrong [as soon as]/[when] they come back.

That's also fine; it's just a different way of saying it.
Comments  
First of all, it must be "If I were you". Being someone else is clearly a hypothetical situation (you can not really be her) and therefore requires the subjunctive mood.

As for the part of "when they come back", let me quote a website on verb tenses (saves me typing Emotion: smile):

No Future in Time Clauses

Like all future forms, the Simple Future cannot be used in clauses beginning with time expressions such as: when, while, before, after, by the time, as soon as, if, unless, etc. Instead of Simple Future, Simple Present is used.

Examples:
  • When you will arrive tonight, we will go out for dinner. Not Correct
  • When you arrive tonight, we will go out for dinner. Correct
So that results in:

If I were you, I would confess my fault to them as soon as they come back."
Students: Are you brave enough to let our tutors analyse your pronunciation?
Thanks you.

Then, the tense use in "That" clause in no.2 and my view about it are correct?


"If I were you, I would confess to them that I did something wrong as soon as soon as/when they come back.
 ferdis's reply was promoted to an answer.