Hi Cloch
While I have sympathy for you, the bank lent you money based on your father's income and your father's assets and your father's name. In a sense, this was a partnership between you and him. This was not a hollow guarantee. If you can't repay your loans, then the bank will probably seek to enforce it against your father.
What is the value of your father's home? Between you, it seems that you have too much exposure to property and your lending is too high.
I think you should try to sell one of the investment properties to reduce your exposure to property and to interest rates. If your father has equity in his home, they will probably allow you to do this and transfer the shortfall on sale to his property.
Will your father be getting a lump-sum on retirement? He could use this to reduce the borrowing.
On a P&L basis, the rent is almost covering the interest on both loans. So the situation is not too bad, as you acknowledge. You need to ask Bank of Ireland immediately to restructure you to interest only. They might or might not agree to this.
I don't know what Bank of Ireland's attitude to guarantees is. I assume that they do enforce them. Against that, most lenders do try to work with their borrowers who are in trouble and they don't like to evict people from their homes.
You could try putting a proposal to them along the lines of your father opting to take the maxium available lump-sum on retirement and putting that against the loans in return from being released from the guarantees. I think that this is as good as you could hope for.
Some side issues
Did you ever have a tracker mortgage with Bank of Ireland? Some customers of Bank of Ireland were entitled to trackers on expiry of their fixed rates, but were not offered them. See
this post for more details.
You can set 75% of the interest on your investment properties against your rental income. You are probably not getting any tax relief on the interest paid on your father's mortgage. So, if you can, you should pay capital off your father's loan before you pay capital off your own loans - assuming interest rates were the same. The bank might not agree to this as your father's mortgage is probably not in negative equity.
Check if you should be getting tax relief on the interest you pay on the interest paid on your father's loan to you. Not sure what a "family investment" is. If the original loan qualified for tax relief, then a loan taken out to refinance that loan, should also get tax relief. If you are working abroad, this might not be of any relevance.