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 someone who eats or drinks thinking that the sun has set, then realizes that it has not yet set?
Whoever eats or drinks believing that the sun has set, then later discovers that it has not yet set, their fast is invalid, and they must make up that day after Ramadan. It is not permissible to break the fast before confirming sunset—either by seeing it, through personal reasoning, or by relying on the statement of someone trustworthy in their religious commitment.
Does passing wind, from the anus without a smell, invalidate prayer?
If a person is certain of having passed wind even if it was with no smell, then both his/her ablution and prayer are invalidated, thus he/she should remake ablution and re-perform prayer.
I have a brother who is harsh in his dealings [with me], and many problems have occurred between us, and I do not intend to reconcile with him. What is the ruling of Islamic Law on that?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is not permissible for a Muslim to abandon or boycott his fellow Muslim brother for more than three days. This is based on the saying of the Messenger of Allah, peace and blessings be upon him: "It is not lawful for a Muslim to forsake his brother for more than three [days], meeting each other but one turns away and the other turns away, and the better of the two is the one who initiates the greeting (salam)." (Reported by al-Bukhari.)
A Muslim must strive to end such estrangement (hajr), so as not to fall under the prohibition mentioned in the hadith. If he takes the initiative to reconcile but the other party does not respond, then there is no sin upon him. We remind [ourselves] of the saying of Allah, the Exalted: "And let them pardon and overlook. Do you not wish that Allah should forgive you? And Allah is Forgiving and Merciful." (An-Nur/22). And Allah, the Exalted, knows best.