Cursing one's children

Q: Can you please give a detail masala about this hadith:

"Jabir (radhiyallahu anhu) reported: The Messenger of Allah (sallallahu alaihi wasallam) said, “Do not invoke curses on yourself or on your children or on your possessions lest you should happen to do it at a moment when the supplications are accepted, and your prayer might be granted.” [Muslim]

عَنْ أَبِي أُسَيْدٍ، مَالِكِ بْنِ رَبِيعَةَ السَّاعِدِيِّ قَالَ بَيْنَا نَحْنُ عِنْدَ رَسُولِ اللَّهِ صلى الله عليه وسلم إِذَا جَاءَهُ رَجُلٌ مِنْ بَنِي سَلِمَةَ فَقَالَ يَا رَسُولَ اللَّهِ هَلْ بَقِيَ مِنْ بِرِّ أَبَوَىَّ شَىْءٌ أَبَرُّهُمَا بِهِ بَعْدَ مَوْتِهِمَا قَالَ ‏"‏ نَعَمِ الصَّلاَةُ عَلَيْهِمَا وَالاِسْتِغْفَارُ لَهُمَا وَإِنْفَاذُ عَهْدِهِمَا مِنْ بَعْدِهِمَا وَصِلَةُ الرَّحِمِ الَّتِي لاَ تُوصَلُ إِلاَّ بِهِمَا وَإِكْرَامُ صَدِيقِهِمَا ‏"‏ (رواه أبو داود)"

Offering free education on condition that the student gives back a fixed percentage after he begins earning

Q: I want to start a school where I also want to educate poor students who cannot afford education. They will be given admission on the basis of a contract saying that in future when they start earning they will give 10% of their earning to me and in the case where they don't earn, they don't have to give anything. Is this permissible?

Suspended talaaq

Q: I had a fight with my wife and in anger, I told her that if you will do this work again you will be divorced on me.

My question is that if she does that work, will the divorce take place? 

Celebrating birthdays

Q: I want to ask regarding celebrating family kids birthday parties. My in laws are not very religious so if someone's kid in their family celebrates a birthday party or celebrates a birthday party at home, what should I do?

I tell them that birthdays are not allowed in Islam and they even say "yes we know, we just doing it to keep the kids happy they can get toys or clothes on this occasion". If I don't go then my husband and in laws get upset and they tell me that I am not part of the family.