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.
Who is "the poor" entitled to receive Zakah (obligatory charity)?
The poor is the one who has neither money nor a source of living, or has either of them, but it isn`t sufficient such as being in need for a hundred/JDs, and having an income of forty/JDs only.
What is the ruling on attending relatives` parties held in public halls, or hotels since if we don`t, we will be subjected to their admonition?
If such parties involve mixing between men and women, or forbidden acts such as listening to songs with sinful lyrics, then attending them is forbidden from the view point of Sharia since people`s admonition is nothing compared to Allah`s, The Almighty`s, wrath.
Must a person refrain from eating for the rest of the day if they break a fast of a vow (nadhr) or a make up fast (qada)?
Whoever observes a vowed fast (nadhr) or a makeup fast (qada) is prohibited from breaking it without a valid excuse. If they break it without a legitimate reason, they are sinful.
However, they are not required to refrain from eating for the rest of the day, because such restraint is only required out of respect for the month of Ramadan, not for other types of fasting.