In a religious context, sin is an act of transgression against divine law. In Islamic ethics, Muslims see sin as anything that goes against the commands of Allah (God).
As far as your students are from general public who can use the knowledge in good way, and you do not know for sure that they will misuse it in unlawful ways, you are permitted to teach them and give them your skill. If you are sure that a specific group of people will use the skill in unlawful work, then you should refrain from helping them to do unlawful work.
It is a sinful act to give away alcohol to any human being even if you received it as unwanted gift from non Muslim. We must refrain from giving alcohol to any human being because it is an evil and we should not part with it in any way but only to destroy it.
Makruh actions will not cause one to have a sin, but it is possible that one could gain more reward by avoiding them. They are actions which are better to be avoided and disliked.
Furthermore although one will not get a sin for doing a makruh action, there could still be a negative impact for one spiritually. So by avoiding them it could build up one spiritually and strengthen their soul.
May Allah grant you success
You should continue trying to help your friend out of sinning as much as you can and whenever you find a suitable time and circumstance to do that. Even if you advice did not work under certain situation, you should keep trying as and when situation is suitable. The prophets and Ahlul Bayt (AS) never gave up advising people despite all the hardships. No doubt, you should be wise and follow the best ways to advise people according to their level of understanding and their circumstances. Allah says in Quran (Invite people to the Way of your Lord with wisdom and nice preaching) ادعُ إلى سبيل ربك بالحكمة والموعظة الحسنة (16:125).
Thank you for your question. Encouraging people towards what is good and forbidding them from what is not is only to the extent that the person will listen to you. At the end of the day everyone has their own choice and if your advice is not heeded and unappreciated then you do not have to continue trying.
May you always be successful.
Repentance needs real feeling of sorrow on committing the sinful act and firm decision not to do it again. If you just fear the punishment but do not sincerely feel sorry for committing the sin or you did not decide to refrain from doing it again, then there is no question of forgiveness.
Watching pornography would go against the clear command of Qur'an to "lower the gaze", Suratul Noor 24:30-31.
What actually entails a major sin, and what the punishments for those are, is a much discussed and debated question.
I understand that it could be interesting to know whether or not watching pornography would fall into such a category.
However, I would like to highlight the issue from another perspective. Generally, when something is haraam in sharia, it is so for good reasons. There is an abundant amount of evidence showing that pornography is harmful for the persons involved in the filming, for the individual watching, and for the society at large.
Many books have been written on the issue, e.g. Understanding and treating Sex and Pornography Addication by Paula Hall, and Treating Pornography Addiction by Kevin B Skinner.
I would also recommend the following TEDx talk: The Great Porn Experiment
To cut it short, pornography is highly addictive. Furthermore, it can cause serious problems in life in different domains, such as marital intimacy, concentration, carrier, and other areas.
Therefore, I would suggest that one looks beyond the question of major sin or not. The fact is that it is potentially very harmful. These are the dire consequences in this life. I dread to think about the consequences on the soul and the life to come.
May God bless you
Thank you for your question. The times of conception and pregnancy are of special importance to a child's soul and so the sins of the parents during that time do have a negative impact. And Allah knows best.
May you always be successful
No one will be punished for the sins of other person unless he approves it. The person who approves and agrees with any act whether good or bad, will be partner with the person who did it.
The bad effect of major sins falls on those children who agree and support it only and not on those who are against the wrong. Mohammad Ibn Abu Bakr was one of the pious followers of Ameerul Mo'mineen, despite being son of Abu Bakr who took the right of Khilafah from Ameerul Mo'mineen and deprived Fatimah from her right in Fadak.
A Mo'min by the name of Sa'd al-Khair from the family of Bani Umayyah came to Imam Mohammad Al-Baqir (AS) and he was weeping loudly like a woman. Imam asked him: What makes you weep O Sa'd? Sa'd replied: Why I should not weep when I belong to the cursed tree according to Quran (Bani Umayyah)? Imam replied him: You are not with Bani Umayyah, you are with us (Ahlul Bayt), did not you hear what Allah says in Quran (Whoever follows me is from me).
al-Ekhtisas by Shaikh al-Mofeed , page 85.
This means clearly that the children of the criminals are not responsible about the crimes of their parents or grand parents as far as they do not agree with the crime.
You must avoid hurting the feelings of your mother. She does not want for you but the best,so, you should consider her wish even if it seems to you now against your wish, but be sure that success can never achieved through hurting the feelings of your parents.
Listen to your mother and keep her respect, and be sure that Allah (SWT) will look after you and grant you success from unexpected sources, and protect you from unseen dangers.
After doing your best to prevent or stop wrong, you will not be responsible for the sins of others even at your own home. You must do whatever you can, and no more than your ability.
Intentional looking at the sinful items is not permissible. If he looked at it with out intention to look at the bad, it won't be sinful. It always important to be away from sinful acts and be very precautious.