What is the ruling of Islamic Law on a fictitious marriage for the purpose of obtaining citizenship?
All praise is due to Allah, and peace and blessings be upon our master the Messenger of Allah ﷺ.
There is no such thing in our noble sharīʿah as a "nominal" or "fictitious" marriage or divorce. Marriage and divorce are among the sacred ordinances of Allah, and it is not permissible to manipulate them or use them as a stratagem to obtain worldly gains.
The foundational purpose of a marriage contract is the permanence and continuity of the relationship between the spouses — to establish a family, and to bring forth righteous offspring. So sacred is this bond that Allah the Almighty Himself described it as a solemn covenant (mīthāq ghalīẓ), saying {what means}: "And if you wish to replace one wife with another and you have given one of them a great amount of wealth, do not take any of it back. Would you take it in injustice and manifest sin? And how could you take it while you have gone in unto each other and they have taken from you a solemn covenant?" [Al-Nisāʾ/ 20–21]
Accordingly, it is not permissible to resort to manipulation and deception in contracts that Allah, Mighty and Majestic, has described as a "solemn covenant" — all for the sake of material and worldly benefit. Marriage is built upon permanence and does not admit of a fixed time limit. If a time limit is stipulated in the contract, the contract is rendered invalid by the consensus of the jurists. Similarly, marriage is impermissible when there exists a mutual, concealed intention to limit its duration — even if no time limit is explicitly mentioned in the contract — for this constitutes a form of unlawful circumvention of the sharīʿah. This is to say nothing of the lying and deception that such conduct involves, the prohibition of which needs no elaboration. Lying, deception, and fraud for the purpose of obtaining worldly gains are among the gravest of sins.
If, however, the marriage contract is first concluded in a valid sharʿī manner and then registered civilly, it is sound and fully valid. And Allah the Almighty knows best.
What is the ruling on doubting whether one or two prostrations were performed?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
If a worshiper is in doubt regarding the number of units (rak'ahs) or prostrations (sajdahs) performed, he must build upon the minimum (i.e., assume the lower number) and perform the prostration of forgetfulness (Sujud al-Sahw) before the Salam at the end of the prayer. This is based on the report from ‘Ata’ ibn Yasar that the Messenger of Allah ﷺ said: 'When anyone of you is in doubt about his Salat (prayer) and does not know how many he has prayed, three or four (Rak'at) he should cast aside his doubt and base his prayer on what he is sure of. Then, he should perform two prostrations before Taslim (salutation). If he has prayed five Rak'at, they will make his Salat (prayer) an even number for him and if he has prayed exactly four, they (i.e. two prostrations) will be humiliation for the devil..' (Narrated by Abu Dawud).
It is stated in Al-Muqaddimah al-Hadramiyyah: 'If one doubts [whether he performed] a bowing (ruku’), a prostration, or a rak'ah, he must perform it and prostrate [for forgetfulness], even if the doubt is removed before the Salam—unless the doubt is removed before he performs what would potentially be an addition. Thus, if he doubts whether he prayed three or four, he is obligated to build upon the minimum.' And Allah the Exalted knows best.
Is it permissible for one who sacrifices on behalf of another, with the latter's permission, to eat from the sacrifice?
It is permissible for someone who sacrificed on behalf of another with their permission to eat from it with their permission, and they stand in their place (act as their representative) in distributing it.
It is stated in Nihayat al-Muhtaj ila Sharh al-Minhaj (Vol.8/P.141): "And he—meaning the one sacrificing on his own behalf, provided he has not apostatized—has the right to eat from a voluntary sacrifice and his sacrificial gift; rather, it is recommended. As for an obligatory sacrifice, it is forbidden for him to eat from it, whether it was designated as such initially or as a liability in his dhimmah. And excluded by what has preceded is if he sacrifices on behalf of another, or if he apostatized, then it is not permissible for him to eat from it, just as it is absolutely impermissible to feed a disbeliever from it."(The text I found indicates the impermissibility of eating) ???
And it is stated in Hashiyat al-Jamal ‘ala Sharh al-Manhaj (Vol.5/P.262): "If a person offers a sacrifice on behalf of a living person with their permission, does he act as their representative in distributing it—on the grounds that permission to sacrifice is permission to distribute it—or does it depend on their explicit permission? This requires consideration, but the first view is not far-fetched." 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.