but then Id have to pay the interest to the bank so I would end up paying more in the long run.
.....sorry to be so basic about this but based on the figures above of €7,500 rental income and €6,000 to my parents how much tax would I be liable to pay? thanks
It depends entirely on what the €6,000 is. As I said already, you only get a deduction for the Interest element of the repayment (and even at that, only 75% of the interest is allowed as an expense). So, if the 6,000 doesn't include any interest then none of it is an expense.
If your parents loaned you 60,000 and you have to repay them 6,000 p.a. for 10 years (a total of 60,000), then there is no interest being paid, so none of the 6,000 is an allowable expense.
If your parents loaned you 60,000 and you have to repay them 6,000 p.a. for 15 years (a total of 90,000) then you would be paying interest. In order to know exactly how much interest is contained in any one payment / year, you would need an amortisation table
http://en.wikipedia.org/wiki/Amortization_schedule. (In this example, to pay 90,000 back over 15 years on 60,000 borrowed, you would be paying roughly 5.8% interest. In year 1 the 6,000 repayment would be: Interest €3,413 , Capital €2,587. In year 15 the 6,000 repayment would be Interest €185 , Capital €5,815.)