A single member LLC is a disregarded entity, meaning that you and the LLC are the same and you file one tax return. You can hold investments in an LLC but you pay the exact same taxes as if you held them as an individual. (LLCs are creations of state law and are not recognized in federal law, so the IRS treats them as sole proprietorships for tax purposes. You and the LLC are the same thing.)
You can't move jointly owned property into a single member LLC unless the other owner(s) surrender their ownership rights. If we suppose that you had a joint broker account with your spouse, and you transferred ownership of the stocks to your single member LLC, does your spouse know they are no longer a joint owner?
What you seem to be trying to do is lower your taxes with a misunderstanding (at best) or an illegal scheme (at worst). Please get professional advice.
