I am rather seeking legal advice for my father.
Lawyers should not dispense legal advice on internet message boards (see the Forum Rules of this site), and your father should not be the slightest bit interested in any "advice" obtained second hand off the internet.
My father . . . has seeked extrordinare wealth with his own small business.
Recently, for my own sake won't say how, but I retrieved all of my mother's data including texts, photos, voicemails, snapchats, insta, etc. new and deleted since the phone was first used.
You're aware that you just admitted in a public forum to having committed a crime, right? Since, to quote your own words, you "care about what's legal," this ought to be rather troubling for you. On the other hand, that you committed this crime suggests maybe your statement that you "care about what's legal" is less than completely truthful.
is it possible that if my father could "keep" the marriage for the next few years that he could slowly start depositing large amounts of money into either my brothers and or my own savings accounts for "Future Savings" or even if it were "for a house in the future" without flagging some kind of external legal power that something could possibly be going on?
I have no idea what you're thinking about here, but there is no "external legal power" that will care in the slightest that he is giving money to you and your brothers. The only exception to this would be the IRS, who will care that taxes are paid on the interest in any savings accounts and, if applicable, that the gift tax rules are followed.
since no divorce has been filed would it really be "strange" or "illegal" for my father to deposit large amounts of money into our accounts on a regular or possibly annual occasion?
"Strange" is not a term that has any legal meaning. No, it would not be illegal. Note, by the way, that "large" is an ambiguous term.
now he's the one getting screwed in the end by my mother.
He is? Nothing in your post suggests this is the case. What makes you think this is true?
By the way, while what you're proposing isn't illegal, any community property that your father gives away without your mother's agreement will be chargeable against him if/when they get divorced. You also realize that giving money to you or your adult brother is no different than giving it to your mother, right? If he gives you money, you aren't obligated to give it back to him.
If your father wants to get a divorce, he should consult with a local family law attorney.