NickM said:
Perhaps he would prefer that they didn't. Why does your mother's desire to contact him overrule his desire not to be contacted?
I'd say it was 50/50 - if she can only get him at work, then it seems fair - she gets her 50%, he gets his at home.
Although I get on great with Mum, and sister, and adore nephew Oli (which has taken me by surprise, since I wasn't really into kids in a big way, but I find watching him develop is fascinating), I have an aunt and uncle-by-marriage I pretty much have nothing to do with, in Canada. So much so that watching the Terry Prachett thing about Alzheimers recently, it never occurred to me until a week later to remember that my aunt has just been diagnosed with it. So, not the sort of thing you send a congratulations card for... I suppose, if Mum (her sister) wanted me to make contact, I would, but for Mum's sake really.
I think a simple congratulations email would be easy enough to send, even if it was a bit through gritted teeth.