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.
Is it permissible to offer an Udhiyah on behalf of another without their permission?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is not permissible for a person to offer a sacrifice (Udhiyah) on behalf of someone else without their permission, except in the following cases: if he sacrifices on behalf of the members of his household, if a guardian sacrifices from his own wealth on behalf of his ward, or if the Imam (ruler) sacrifices from the public treasury (Bayt al-Mal) on behalf of the Muslims. And Allah the Almighty knows best.
Can someone who begins a voluntary fast break it?
It is preferable for someone who begins an act of worship not to break it.
Allah the Exalted has said {what means}: "and let not your [good] deeds come to nought!" [Muhammad/33].
However, if a person starts a voluntary fast (nafl) and needs to break it, they are going against what is preferable, but there is no sin upon them.
Is it permissible for a wife to refuse to go to bed with her husband (for sexual intercourse)?
It isn`t permissible for her to do so unless for a sound reason.