Is an unregistered marriage, if it has witnesses, a dowry (sadaq), and a deferred dowry (mu'akhar), considered fornication? And is the official contract invalidated if it was done under duress and the legal guardian refused?

It is forbidden for a woman's guardian to prevent her from marrying, thereby pushing her into sin. A marriage without a guardian is invalid. A woman whose family prevents her from marrying should take her case to court so that the guardian is compelled to marry her off, or so that the recognized شرعي (Sharia) judge undertakes her marriage. Repentance is obligatory for entering into an invalid marriage contract. If the second marriage was undertaken by the paternal uncle with the father's permission and in the presence of two upright witnesses, then it is valid, and their statement that they were compelled or that the contract is invalid does not affect its validity. The woman does not need an 'iddah (waiting period) of 'istibra' (clearing of the womb) from the previous intercourse that occurred under a misconception (shubhah).