What should I do, as I swore falsely upon the Book of Allah concerning my harassment of one of my محارم (unmarriageable kin), fearing the disintegration of the family, and I am remorseful and have repented to Allah?

You must conceal your own actions and not confess to your father the heinous sin, because among the matters in which lying is permissible is denying a sin to conceal oneself or others, as long as it was not committed openly. If you are compelled to swear an oath, use dissimulation (tawriya).