They planned it for quite a while. In fact I remember BIL discussing with me two years back during Christmas holidays.
On Wednesday, BIL took baptism in Catholic Church with a Christian name of Benedict (the name of the current Pope). Primary purpose is to avoid confusion about the religion of the kid(s) on the way! (If you already didn’t know it is a inter-religious marriage).
They also ratified their marriage – they got married in a register office, not in a church.
It was a family event and an important one for parents and sister – I really don’t care, these are just symbols.