Is it permissible for an engaged couple to complete the marriage despite family disagreements, and is that considered disobedience to parents?

It is permissible for the suitor to sign the list of movables without his parents' knowledge, as long as it does not violate Islamic law or cause him harm. This is not considered disobedience to his parents. It is preferable, however, for him to try and convince his mother of this, and he must honor his mother and obey her in what is good.