Husband

Bismihi ta'ala

The divorce would not be valid if that was the case, and the best thing to do is for you both to refer to a qualified scholar for marriage counselling, and if no solution can be made and there is no hope for reconciliation, then husband can inform the qualified scholar and conduct the divorce in the correct way, meeting all the valid requirements, and give a document for it as well. 

And Allah knows best

Bismihi ta'ala

There is no 'iddah for the wife to observe while "filing" for divorce. She must observe 'iddah only after the Islamic divorce is recited. When the talaq is recited, her 'iddah period will be three menstrual cycles. 

And Allah knows best

Bismihi ta'ala

If she becomes Muslim, her marriage is automatically be nullified, should her husband not convert as well. She will need to observe 'iddah as well.  

Of course, this is a serious decision that she needs to deeply think about, as leaving her husband might not be an easy thing to do.

And Allah knows best

Bismihi ta'ala

Yes, the 'iddah period must still be observed by the wife, even though a long time has passed from their separation, as long as she is not ya`isah. 

It is three menstrual cycles, and she does not necessarily need to do anything. The only thing she cannot do at all is get remarried during this time. 

Please refer to detailed Ahkam books for further explanations.

And Allah knows best

Bismhi ta'ala

This is going to be a choice the husband makes. Of course, you must understand how difficult it would be for him to trust you again, or to forget the incident, and it might continue to be brought up, especially if you have an argument. 

He might even accuse the children of not being his, and so on. 

Therefore, if he forgives you, which is possible from a shar'i perspective, you must both navigate correct solutions to deal with the infidelity and how to avoid it in future, from both sides.

And Allah knows best

Bismihi ta'ala

Yes, of course you can do that, and it is rather recommended to do charity work and noble deeds on behalf of others, alive or passed. 

You will indeed be rewarded equally, if not more for your consideration of doing good deeds on behalf of others.

And Allah knows best

Bismihi ta'ala

No, a civil divorce does not take the place of a shar'i divorce.

What this husband must do is find out if his violation of law of the land is sinful and haram.

But nonetheless, it will not affect the shar'i legitimacy of the marriage, and they would still be husband and wife from a shar'i perspective. 

And Allah knows best.