What are the legalities. when a spouse unkowingly access money from your account?
Depends of what State. If the incident occurs in a "common law"
state; that is to say that property of married persons is
considered "joint" property, nothing.
If a spouse "unknowingly" accesses money from the account of a
"spouse", unless there is a written agreement, such as a prenup or
separation agreement, there is no crime.
By mere virtue of the fact that the spouse COULD access the
money, negates any claim the other spouse could make.
"Unknowingly" implies without knowledge. It is not possible to
access money "unknowingly", thus I take your meaning to be the
identity of the account holder was unknown.