op. I am a lawyer. please go see a solicitor to discuss all these: will, securing your 26yo in the event of death and generally to understand your situation. you have many Qs which require professional answers. you can then decide to tell your spouse whatever you want, after getting legal advice.
I married whilst owning assets worth just over 2 mil with dh owning less than a 3rd of that- we married soon after meeting. I don't have kids. I don't plan to divorce as I like him enough even when he is at his worse (according to me.) I would not have married if I thought I would even 5% want a divorce.
however, in the midst of first months of love, hope etc when we married, it was my twice married friend I owe my sanity to, as she insisted I got a prenup (I fully understand the legal implication in England so don't need lessons). she had knowledge of my financial independence secured through real sacrifice and hard hard work. I hid my embarrassment and asked for one. glad I did.
no fault of his own, but a relative ran his company down soon after marrying that at some point I wondered if he married me for my financial position. it was dreadful especially as I had lost my equally financial secure dp in a sudden death. however, as I didn't marry him for his financial standing which he was working on improving, it was the knowing I could walk away intact- short marriage, no kids and tight prenup that kept me going whilst getting my head around his sudden bad situation as soon as I was on board. read: while putting some spine in him to get rid of the person running his company down and affecting his new bride.
so, it pays to get legal advice even if you do not intend to separate. I simply refused to contribute to any outgoings- designed to let dh not feel he was being bailed out and therefore deal with his relative. it worked and dh is now back in charge of his business and rebuilding it. I now reminding him he was lucky I didn't marry him for his money, as I would have cleared off while he was appeasing his relative; although I was also not prepared to live in his pressure cooker forever.
good luck op