Only a handful of people can make laws, nobility and magistrates (mayors of a settlement with a courthouse).
other aristocrates can not make laws.
Then comes the enforcing part, as of today information at our disposal it will be a bit of the same, it will not be up to every body to enforce laws. Nobility will be able to as they make the laws, along that line it is only natural that magistrate will be able too, then barons, knights and sheriffs will also be able to enforce law.
Now even if laws are contracts (implicit ones), they are not the only ones and each party in a contract can enforce his part on the other party if they do not follow the contract be it explicit one or implicit.
So a mayor might not have the power or authority to enforce county's laws or to make his own settlement laws, but he'll have the authority to enforce city planning and settlement tax collection.
keep in mind that this part law enforcement is yet not totally explicit, what about settlement guards ? on who's authority will they act ? what set of laws are they entitled to enforce if any ? can any one that grab a bounty his empowered to enforce it or do you need some permits or title ?