This is an opinion only, but I think you're subsidising his retirement ! You pay every month now, and then pay €180k in three years for a house that when he purchased it was possibly only worth €175k ? (You need to provide details of the value of the house)
What makes you think you'll get a mortgage in three years time ?
From a taxation point of view, there is possibly some juicy tax-planning which can be availed of here in a scenario such as this. I'll post later on this.