Google "First Time Buyers Ireland Revenue" - they have a very good section of the rules applicable.
I think its fair to say in general:
1. If there is more than one purchaser and one only is a ftb - it is likely that full stamp duty will be payable.
2. Where a married couple is involved it is unlikely that (a) a lender will lend to one only and (b) allow title in one name only. In the event of a split and a wrangle over the family home, you can just imagine the fun and games unless the property is in joint names and the mortgage is in joint names.
mf