On the old family home, there will be no CGT as you can have inheritance up to 400k tax free. So this does not need to be taken into account.
Rental bought at €265k and lived in for 10 years (+1 added for tax), rented for 8, then the cgt will be 33% of 45% of the gain, so circa 15% (€18k)
I can see both angles - pain for a few more years and then move to the original house and use inheritance to pay off mortgage and at that point aggressively contribute to a pension to avail of the tax advantage of doing so.
Or free yourself of debt which would allow contribution to a pension fund of at least anything you are paying high rate tax on and allow you make improvements to your dad's place.
I'd probably go for the latter especially if the current tenants wish to buy as it would be near hassle free.