Our children have names with same first initial. Our second had no name at all until he was six weeks old as we couldn't agree, so finding a comprimise was more important than the initial.
When the third came along we argued throughout the pregnancy but eventually I insisted name must be English and old while DH's conditions were that the first letter would be the same as his siblings so that 'he won't feel left out'. So we found a name that way.
The post isn't an issue - they have different middle initials and it is usually obvious who it is for.
The only time it ever caused a problem was with the bank, funnily enough. One cashier asked my son about his 'other account' and would he like it incorporated with his regular account.
'Sure' says son (aged about 17) 'Strange how I had money I didn't even know about . '
Cue a hysterical phone call from my daughter at university, 'My account's been closed!'
When the mess was sorted out, the bank said it was an easy mistake to make but would retrain the staff anyway... 