Is it obligatory to inform the fiancé's father or the fiancé himself about a previous pelvic fracture that has completely healed and does not affect marriage or pregnancy, and do they have the right to annul the engagement because they were not personally informed of this?

It was not obligatory for you to inform the suitor of your previous illness, especially since Allah has healed you from it, nor to inform his father. If the marriage did not transpire, do not despair, for it may be good for you. Entrust your affair to Allah, and ask Him to grant you marriage to a righteous man; as Allah Almighty says: "And perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not." (Al-Baqarah: 216).