Is it incumbent on a father to cover the marriage costs of his son if the latter couldn`t afford them?
The son should seek the help of his relatives in order to convince his father to do the aforesaid, and the father should make sure that his son doesn`t commit fornication through helping him to get married, and Allah will reward him for doing so.
What is the ruling on one who slept while firmly seated on the ground, regarding nullification of ablution?
The default ruling regarding sleep is that it nullifies ablution. An exception to this is one who slept while firmly seated on the ground; his ablution is not nullified by sleep if he wakes up while still firmly seated on the ground. And Allah the Almighty knows best.
What is the ruling on the intention of fasting, where is its place, and when is its time?
The intention is a pillar of acts of worship; it is essential, and worship is not valid without it.
Its place is in the heart, and verbalizing it is recommended so that the tongue reminds the heart. Its meaning is to be determined to abstain from nullifiers of fasting during the upcoming day with the intention of worship and obedience to Allah Almighty. This meaning is naturally present in every Muslim on every night of Ramadan, so there is no need for obsessive doubts. If one says, "I intend to fast tomorrow for the sake of Allah," it removes any doubts.
Its time is from after sunset until before the true dawn.
Is it obligatory to make up all missed prayers?
All praise is due to Allah, and peace and blessings be upon our master the Messenger of Allah ﷺ.
Making up missed prayers (qaḍāʾ) is a sharʿī obligation, established by the practice of the Prophet ﷺ himself — when the disbelievers preoccupied him on the Day of the Trench and he missed the ʿAṣr prayer, he made it up afterward. This is further affirmed by the ḥadīth: "Fulfil what you owe to Allah, for Allah is most deserving of being fulfilled." (Reported by al-Bukhārī.)
Accordingly, a person who has missed prayers should set aside his voluntary and Sunnah prayers and replace them with make-up prayers in their stead. There is no objection to making up one missed prayer alongside each obligatory prayer that is performed — praying the equivalent missed prayer together with each current obligatory prayer as a practical and manageable way of gradually clearing one's debt of missed prayers. And Allah the Almighty knows best.