Is the prayer of someone who didn`t face Quibla (Ka`ba direction) valid?
All perfect praise be to Allah,The Lord of The Worlds. Facing the Quibla is a condition for the validity of prayer, and the prayer of the person who hadn`t faced the direction of the Quibla is invalid, and he is obliged to repeat it. And Allah Knows Best.
Should missed Sunnah prayer be made up?
Making up missed voluntary acts of worship is from Sunnah.
What does "All the deeds of the son of Adam are for him, except fasting" mean?
The Prophet ﷺ said: "Allah, the Almighty, said: 'Every deed of the son of Adam is for him, except for fasting; it is for Me, and I shall reward for it." [Agreed upon]
This means:
● Every deed of the son of Adam may be affected by showing off (riyaa’), except fasting, because only Allah knows whether a person is truly fasting or not.
● The reward for all deeds is known—one good deed is multiplied tenfold—except fasting, as only Allah knows its true reward.
Is it permissible for a young man and a young woman to enter into a covenant as a married couple without having a true seclusion (Khalwah) until their marriage contract is officially concluded?
The relation which isn`t based on a marriage contract is forbidden, and entering into a covenant as a married couple is unaccounted for and is from the evil suggestions of the devil.