What is the ruling of the Sharia on my marriage to my maternal uncle's widow, knowing that I desire this in emulation of the Prophet, peace and blessings be upon him, in his marriage to Lady Khadijah, and that my family rejects this marriage, and what should I do to convince them, and should I continue visiting her?

Based on the prophetic narrations, a marriage contract is not valid except with a guardian (wali), and a woman who marries without her guardian's permission, her marriage is null and void. It is not permissible for a man to be alone with a woman who is not a mahram (definition) to him, for Satan is the third of them. Any forbidden relationship must be cut off immediately, and one must repent to Allah. If you wish to marry this woman, then the matter should be approached through its lawful channel, which is to propose to her, and then her guardian will solemnize the marriage contract for you.