Amanda Bynes' engagement ring is an Amazon bargain ... and her family is going to block her from tying the knot. Sources close to the family tell TMZ ... Amanda will never legally marry her fiancee, Paul Michael, because her mother holds the keys to marriage and she doesn't approve of her daughter's engagement. Amanda's mother is her conservator, and we're told Amanda cannot get married without her conservator's consent. Our sources say the family feels it's not in her best interest to be married -- they haven't met Paul -- so a wedding ain't happening.