A relative of mine got married while her father was sitting shiva. Both uncles and aunts were told that they were allowed to go to their nieces wedding even though they were in middle of shiva. They were allowed to go for the chupa and then had to leave afterwards.
Another relative of mine got up from shiva 2 days before her wedding. The wedding was not pushed off and e/t went on as normal. I don’t know about the siblings of the kallah though, what their limitations were.