fixed percentage

Q: I have paid 50% money for owning a business firm and the owner put a condition that I must pay the balance 50% within 6 months’ time and I have to give the money from foreign country where he is working. I can run/own the business only after paying the full amount. After 5 months, I asked my friend to join the partnership with this business by paying the balance of the money from a foreign country and he is ready to join also. However currently the value of this business is increased during this 6 months duration. So, can I reduce his partnership percentage to 30% as per current value of business firm and actually he paid 50% of the total value (It means he has to pay more money than actual value that I brought as per current market price). Is it become permissible as per Islamic rule?

Q: I have a question on putting investment.

We have a group of around 45 people and each guy is putting a total of 1200 AED for 1.5 years. And one guy among us is buying a Limo Taxi to run as per Government Rules and every month he will be giving us 15% of the money after his expenditures like room, food, etc.

Total 55000AED only will be from our group of people, and remaining cash needed-the guy who is purchasing the car will be arranging. As per him, he will be paying back monthly to Emirates Transport, a Government Authority, the cash he will arrange. We asked any interest in that, he said he is not sure about it.

We will be getting 15% from the 55000AED amount we are investing, and this is fixed percentage, and the amount may increase or decrease based on how much work he will get with his taxi. But the percentage will be same 15%.

I would like to ask you, if in the amount we are investing there is no interest, will it be haram for us? Because, in the amount this guy is arranging, he may be paying monthly to Authority with interest.