Across two threads and three pages of responses from the OP, there are still some pretty pertinent questions that haven’t been answered:
Why, if there’s such a long term split in the family, did the bride not only invite her uncle, but ask him to give her away? That’s a pretty integral role in the wedding. Unless the bride is super-traditional, there’s no obligation to choose a male relative or a man at all - her mother could have done it. She must have actively wanted her uncle.
Why, for the same reasons, did OP’s husband say yes? Why would you actively choose take part in a wedding when you have a terrible relationship with the people involved?
The OP didn’t want to sit with strangers - but there wasn’t anyone there who she knew, other than those at the top table. So did she expect to be there - even though she describes the mother of the bride as a bitch and a cow, and apparently she’s hated her for 60 years?
One obvious answer covering all questions comes to mind - that being that the OP’s husband doesn’t have any issue with his niece, and vice versa. And as such, she wanted him to be part of the wedding, and vice versa. And the issue is actually with the OP, who came as part of the package.