You get a 3k small gift exemption each year in relation to all individuals who give you a gift so if the loan is from both of your parents' funds, the small gift exemption is €6k.
The deemed gift is calculated using the interest your parents would get if they placed the money on deposit which is unlikely to be be €3k not to mind €6k, so it will be covered in full by the small gift exemption.
There is therefore no need to declare it. However, in case of any queries from the Revenue it would be best if you and your parents put in writing that this is an interest free loan, repayable in four years. Everytime you make a repayment, you should ensure that you keep evidence of this (eg bank statements showing the transfer).