Please, don't quote laws from cases you think apply. I am aware of the standard(s) to be a putative spouse. We need to deal in facts first.
I think the argument is irrelevant as to whether one or both parties agreed they were married. Obviously, issues of gay marriage would come to mind, which California explicitly is still fighting. The fact here is there is doubt as to whether or not there was honesty and sincerity. In fact in further questioning my sister said it was the husband who supposedly went to drop off the application both times, it was also him who hired the officiant which incidentally cant be found.
So, the person who needed a valid marriage, under law, to be a citizen and you claim that was his purpose to this, didn't honestly and with sincerity believe he was married? Why, then, did he do this? Before you said there was no witness, now he can't be found. Which is it? This is not going to be a legal win or loss, it will be a factual one. While I understand there is a difference between believed and agreed (The gay marriage is a good example.) there was a license taken out, there was a witness and, apparently some ceremony or purported signing. After that, both parties lived together as being married. Is it your claim they were just living together and both knew that?
The reason why in my humble belief an Unclean Hands claim is that it is an affirmative defense by either the petitioner or respondent which precludes equitable relief which is what a putative marriage is entitled to. Equal share of property, spousal support etc. Therefore, as it Ceja case is currently pending appeal to Supreme Court of California, there is a real question of law.
You said both parties had unclean hands. Can it be an affirmative defense if both have them? How did the plaintiff benefit from his unclean hands? Do you have any facts to prove them other than Sister's testimony? Because it seems to benefit sister to have committed fraud far more than Husband and just testimony is not going to really sway.
B. The parties intend for this Agreement to become effective upon their marriage or cohabitation pursuant to the laws of the State of California, including any Uniform Premarital Agreement Act, or other applicable laws, adopted by the State of California;
The Agreement is effective upon the marriage, you are claiming no marriage. If a putative marriage, there is no marriage. Now, before you say it (and what I alluded to before), the "or cohabitation" is irrelevant. Tell me why.
(a) For purposes of this agreement Spousal Support is defined as any real money to be exchanged for the benefit of the other. Which will lawfully include money in the form of income earned by either party, property, or other convertible instruments including bank accounts, pensions, or interests earned. Such Support is waved by both parties.
(b)Both parties agree to waive alimony, palimony, or any other avenue in which to gain support from the other with the exception of support of a child, as it is defined under California law. This waiver can only be terminated by both parties agreement in writing. In the event of a child support under this section shall only be interpreted to mean support in the financial obligation of one party to the other on a equitable award that a court may award to make the parties whole for the purpose of child rearing. Such waiver has been thoroughly explained to both parties and both parties have been made aware fully that they have no right to any form of financial support of the other in the event of nullity, dissolution, or divorce or otherwise separation from the other. This includes any form of Temporary Support pending a final order in the event of divorce, annulment or dissolution. Such support is waived by both parties.
You're still missing a piece of the puzzle.
F. Each party has had the opportunity to retain their own lawyer and receive independent legal advice regarding the terms of this Agreement; both parties freely waive advice of independent counsel and enter this agreement with good faith and consideration.
We could say the agreement was unconscionable, but we don't know the facts of the situation. It would certainly lend itself to being considered such in many instances if there was an inequality between the parties. But, there is a huge problem STATED RIGHT IN THE AGREEMENT. You don't have to read the whole thing. I provided the relevant sections above.
Sister should get an attorney. If she does not have one, she should ask for a continuance to get one. You are not helping her.