Obviously not for siblings, but what about for cousins? We have loved Wilf since I was pregnant with my eldest, but have always discounted it because my sister in law's little boy is called Will (Will on birth cerificate, not William). He will be almost 11 by the time we have our baby, so they won't be hanging out together as mates for quite some time, but we do see them fairly regularly. I am really struggling to find anything I truly love and feel like I am settling for something that I do like but that isn't quite right, so I'm really loathed to discount anything. We would probably have Wilfred for the birth certificate, but maybe not? Needs thinking about. My sister in law is very nice and laid back so I don't think she is likely to mind, but I worry about it getting confusing!
It probably will be confusing at family events, but then you have to weigh that against it being the name you love. IMO I would put Wilfred on the birth certificate then he has choices of nn when he's older.
They are similar but I wouldnt worry about it. If they were similar ages it might be more a problem but 11 years is a big gap. As close as you and your sister, and family, might be its unlikely theyll become best mates at least not for a while and Wilf will have established his own personality and place in the family by then. Id maybe let your sister know in advance, but be careful it doesnt sound as if youre asking for her approval.
It's my hubby's sister, not mine btw - not sure if that makes any difference!
We've sort of agreed on Nathaniel, but it isn't quite right and I keep wobbling about it. I like short names and find it a bit long. We want to avoid 'top flight' names if possible (though daughter has a top 50 name, so not totally opposed if it's right), but don't want anything too unusual or anything that is easily pigeon holed by 'class'. Older children are Jude and Scarlett. I'm very difficult to please!
I'd go for Wilfred (not Wilf) as he would have a choice of what to call himself when older and it would not at all be the same as his cousin Will. Then you can call him Wilf at home and if it gets confusing at family do's then call him Wilfred there. I don't think it sounds like your SIL would be put out at all. Do what you like best or you'll be upset for years.
And for the (weird) record my really good friends have a dog with the same (abbreviated) name as my DD! I mentioned it before she was born and they were absolutely okay about it. In fact we call them "Bonzette-1" and "Bonzette-2" when they are together. (dog gets a bit confused though )
I think its fine for two cousins to have similar names. If they were siblings it would have been a bit confusing, but I think it's fine in your circumstances. (And imo you should only put Wilfred on the bc if you like that name as well as Wilf... but I know that is a contentious issue so I'll tip toe away now ).