No "attachment" that I can see...
In brief: if you weren't married, the law says that is what is yours is yours, what is hers is hers, and what you own jointly you own equally unless there is something to prove otherwise.
If you own 3 properties as joint owners in equal shares, you are each entitled to the amount that you would get if all three were sold and the proceeds divided equally. If you choose to achieve this by redistributing the properties between you, and make any necessary balancing payments, that is fine, but neither of you can insist on any settlement that gives the other less than their full entitlement (half the total values).
In the event of dispute, the court will, bluntly, order a sale of the lot and split the proceeds equally.
Neither of you are entitled to maintenance or any other financial support from the other: there is no such thing as a "common law marriage". You are two property owners who previously lived together, that is how the court sees you, nothing more than that.
You absolutely don't want to remain on a mortgage for a house you aren't going to live in or have any substantive interest in, that's keeping the liabilities and giving up the
benefits.
She may be liable if she has been diverting money but this can get complicated, get advice.
The situation over the BTL account is also difficult, but at the very least you can insist that any future income goes into a joint account rather than one in her sole name, if its as much your income as hers.