I think getting married and not telling any friends and family is bound to lead to some upset – it’s just a question of how much. I wasn’t invited to my sister’s second marriage, which didn’t bother me, but I can understand why some people would get upset.
The mother in law, for instance, may find it deeply embarrassing as then all her friends will know about it.
If I were to ever get married, which I won’t, I would let people know, but have a very small wedding, maybe 10-15 people, then a party a week after with everyone invited.