I find it hard to understand the issue as well.
I recently sold that property
Did you ask the bank's permission before you sold the property? Did the solicitor allow you to exchange contracts without permission from the bank?
When you say you have "sold" it, what do you mean? You have agreed to sell it - I presume you have not exchanged contracts.
How much will you get from the sale? Why don't you pay down the mortgage?
It seems perfectly reasonable for them to ask for the mortgage to be paid off in full before releasing the security.
So they just want €97k paid off, that is decent enough of them.
It's almost impossible for a lender to repossess a family home, so they are not interested in having it as security, even if it is more valuable.
Have you considered selling your family home to help your son buy a house and pay for the wedding? If it's not given as security, you will be able to do so.