Do I need to send a wedding gift if we hardly know the people and we decline the invitation?

My boyfriend of 10 years and I have been invited to a wedding. The bride is a second cousin of his who he has only met once. I have never met either the bride or groom. To be honest, we’re not sure why on earth we were invited. If we decline, would we still be expected to send a gift even though we don’t know these people at all??

I understand that gifts are a nice gesture and not expected at all…but in this case, I am really stumped.