Is permissible to buy/sell with non-Muslim?
Yes buying/selling for a Muslim with non-Muslim is permissible as regards what is lawful.
What is the ruling on swearing on the Holy Quran and breaking that oath?
It is impermissible to swear on the Holy Quran in vain, and it is also impermissible to subject it to such an act since breaking the oath after swearing on the Quran entails an expiation.
Is it permissible for the guardian to give Sadaqa (voluntary charity) from the money of the orphans?
It is impermissible for the guardian to donate from the money of the orphans because he is entrusted with the safekeeping of that money, and is prohibited from donating it.
What is the ruling of Sharia on marrying a Jewish woman, dealing with the Jews, and going to Israel?
All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It is allowed for a Muslim to marry a Jewish or a Christian woman provided that this doesn`t affect his religion. As for dealing with the Jews who are outside Palestine, it is the same as dealing with the Christians; it is permissible as long as it doesn`t harm Islam. As for dealing with the Jews who are inside Palestine, the ruling differs depending on the persons themselves and the situations. By the end of the day, a believer`s heart leads him/her to what is good. And Allah The Almighty Knows Best.