I think that your solicitor is wrong on this one.
Let's say you have a house worth €250k and a mortgage of €300k.
If effect, your husband is paying €150k for €125k worth of house. There is no gift here and I really don't think you need to pay for tax advice on what is a fairly routine transaction.
He and you will be deemed to be buying 50% of the house from your ex, so you will have to pay stamp duty which is 1% of €125 or €1,250.
You and your partner must do up an agreement for the purchase and the mortgage so that, if you split up, you will know where you stand.
Brendan