giving interest and taking interest

Q: I am a 26 year old man with a job in the I.T field alhumduallah. I am currently living with my family and they are making lots of plans to buy a building with interest. They have already found a building and are planning to move in and live there. I don't want to be apart of interest and i never imagined being in this situation. As the youngest brother(i have 3 older brothers) my opinion doesn't hold much weight in the family. They think i dont know anything. They would like me to help with the payments in order to pay the building off as quickly as possible. Will i be sinfil for helping them make payments and what is your opinion about living in a house in riba? I can take care of myself as i am financially stable. And my teacher also said i can live at his madrasa for free and he recommended me to ask you. The biggest problem i see is that if i move out it may mess my relationship up with the family. 

Q: Could you please explain to me what is interest, riba and usury. If one has the talent to do a halal business (by Allah) and no money, and other has money but he can't do business, the one who is giving the money to the first person for the business and asking him to give a profit of 50% and at last he should return his money. Does this come under interest/riba/usuary. If yes then how should the business situation be dealt with. What does one do if one did that, and falled in a loss.

Q: Can a Muslim take out a usuruous loan to support their family if they are living in conditions that are dangerous such as, if their home is being burglarized and living in a dangerous neighborhood filled with gangs and drugs? Is this a condition of zaroorah (necessity) or haajah (need)? Can one commit a major sin, dealing with Riba (Usury/Interest), in order to get his family away from these conditions. Please advise. 

Q:

1. What is the status of permissibility with regard to student loans? Here in Australia, we have the option of paying back all or some of the loan, but it has some form of interest (indexing) applied to it. These loans are usually taken out by university students.

2. What about those who have already taken out a loan and do not wish to pay back? The Australian law requires a re-payment of the loan incrementally in the form of income tax, which only becomes mandatory if and when the debtor is earning above a minimum yearly salary.

Q: Sending this on behalf of someone: If I buy a property and the bank finances it and I pay a set amount plus interest every month to the bank, is it halaal or haraam?

Q: Is it permissible to do riba transactions with non-Muslims in daar-ul-harb?

Q: Is it harem to give interest?