Quoted Rich Dad, Poor Dad .
Forget that. It is an American book which has very little application in Ireland because of the very different legal systems and tax systems.
Is this what your son is proposing?
Son will buy a house in country and in Spain and will rent them to you?
He will let out your house in Dublin and take the rent?
He presumably continues to live in his current family home?
This is how this would be taxed:
You would pay rent to your son which would be subject to tax. He would get some tax relief for the mortgage interest paid in Ireland. I have no idea what the tax consequences in Spain would be.
You would be getting rental income in Ireland. This would be taxed in full as you have no mortgage interest to set against it. (It would be completely irrelevant that your son is letting it for you. As the owner, you would be taxed.)
Your house would become an investment and when you eventually sell it, part of the gains would be subject to Capital Gains Tax. If you sell it now, there would be no CGT if it's been the family home since you bought it.
The commercial aspects of the proposal are equally terrible
House in Dublin being worth more, it would be his pension.
People should not be buying property "as their pension" unless they do it within a pension fund. If he already owns his family home and if he has a rental apartment, he has enough exposure to property. He should probably start a normal pension to avail of the very generous tax benefits. Direct ownership of property is heavily taxed and is not a good idea.
If your son wants to invest in property, let him do so. It's unlikely that a family home in Dublin would be the best property investment. My understanding is that the best yields are in the apartment sector and lower priced houses generally.
If your son thinks that your house is a good investment in its own right, then he should simply buy it from you at market price with an investment mortgage.
That is much cleaner for all of you and has no complicated tax consequences.