Is informing one's parents about good deeds performed for the sake of Allah Almighty, with the intention of making them happy, considered diverting the deed from being solely for the sake of Allah? And is feeling joy when performing acts of obedience considered a presumption against Allah, even while believing that success in obedience comes solely from Allah?

Informing one's parents about what you have done does not invalidate the act as not being for the sake of Allah, as long as the original intention was to seek Allah's pleasure and you did not intend to seek their praise. Nevertheless, it is advisable to keep good deeds secret if there is no legitimate Sharia benefit in disclosing them, because sincerity is precious and one's intention may deviate. As for feeling happiness when performing acts of obedience, there is no harm in it if it is due to realizing the act of obedience, Allah's guidance, and the reward that is hoped for, based on the Almighty's saying: "Say, 'In the bounty of Allah and in His mercy - in that let them rejoice; it is better than what they accumulate,'" and the Prophet's (peace be upon him) saying: "Whoever is pleased by his good deed and displeased by his bad deed, that is the believer." However, if the happiness stems from self-admiration, then this is a calamity.