Receiving interest on a loan

Q: My friend is asking me for Rs.100 for a business and he is telling me that he will give me the money after 1 week along with 2.3% of the Rs.100, that is after 7 days he will give me Rs.116. Can I take this Rs.116 or is it haram?

Moreover he is telling me how much you give me I will give you after 7 days with 2.3% of your invested money. Please clarify, if it is halal I will proceed otherwise I will not.

Secret nikaah

Q: I am proposed to my long relation cousin. Both of our parents agreed to our marriage. Actually it is their arrangement. Also with their permission we are speaking via phone. But due to my education my parents don’t want me to do nikah right now. My question is, can I discuss only with my future wife (in shaa Allah) about mahram and give that mahram amount secretly and make this relationship to be halal? Or else am I allowed to keep one or two witnesses only and make this relationship halal? I don’t want the blame on my parents because i don’t feel like its their mistake.

Paying interest on debts

Q:

1. I have a very old debt of almost 15 years back that some of the places I have the debt with has written it off and some is still charging me interest. Am I liable to pay this interests?

2. And on the other hand a friend bought things on my account also 15 years ago and the place is still holding me accountable, however the person that bought the goods have passed away. Am I liable for this account?