Do the aforementioned signs—such as ablution, prayer, reciting the Quran, dying while glorifying God, and perspiring, in addition to his persistence in obedience and his brother-in-law's vision of him—constitute evidence of a good ending and a testimony in his favor?

Your father's utterance of the two testimonies (Shahadatain), his death with sweat on his brow, his ablution (wudu'), and his recitation of the Qur'an before his passing are all glad tidings indicating a good end for him. It has been reported that the last words "La ilaha illa Allah" (There is no god but Allah) guarantee Paradise, and that a believer dies with sweat on his brow for the expiation of his sins or for the increase of his rank. And whoever dies upon a righteous deed, his life is sealed with it. If Allah intends good for a servant, He guides him to a righteous deed before his death, and then takes his soul while he is upon it.