I also do not recommend investing in shares due to the risk involved. By risk I mean the fact that you will need the shares to rise in value by the 4.5% you are paying on your mortgage before you even break-even. Based on past performance (although, as has been said many times before on the forums, past performance gives no indication to future performance) of the ISEQ which has more than doubled over the past few years, this strategy would have worked well. However, it is equally possible that the ISEQ may lose alot of value over the next few years. If, in possibly the worst case scenario (however unlikely), the value halved after 4-5 years and you decided to bail out and pay the share proceeds off your mortgage, you would be left with a LTV of around 35-40% at 45 as opposed to the current LTV of 25% at 40. The fact that you will be taking an income from your investments as opposed to reinvesting dividends makes this scenario all the more likely. However, if you're willing to take this risk, the upside is that whatever stockmarket you invest in could continue to rise at it's current rate and you could be paid off very handsomely. Just remember that stockmarkets tend to work in cycles and most stockmarkets are now at all-time highs.
On an unrelated topic, if you are currently paying 4.5% on your mortgage you should look into switching to [broken link removed] who released a very competitive mortgage to the market in the past few weeks. They will pay the costs associated with switching and the rate will be 3.75% for you. This is a saving of 21 euros per month per 100,000. Judging by your figures above, you're current mortgage is around 200,000 so switching will save you 42 euros a month. It doesn't sound much but if, as you say, your regular income is too low to support family at this time, it will be a good start.