What are you insuring them against?
Fire - remote.
Theft - remote. In general, thieves don't rob paintings as they are identifiable and there is very little demand.
If you do want to insure them, then you can get an idea of their value from what you paid for them. Any of the auction houses, such as Whyte's or DeVere's will do a valuation for insurance purposes. I presume that they would charge a few hundred euro for the purposes.
You could also sign up to artprice.com and try to value them yourselves.
But, the simplest thing to do, is to take good photos, measure the sizes, make a note of anything on the back of them e.g. gallery labels. The auction houses would probably tell you quick enough for free, if you need to insure them.