I prefer personally when rates are matched because often my duo partners charge more than I do, and it's honestly more polite and more fair to the provider who charges less, but you can still ask. I've accepted to do a duo recently during which I was supposed to get paid less than my duo partner, it was disappointing but I still did it. However we had to cancel because the client was not respectful.
When I've gotten approached from duos I asked a few companions if they were available on the day of the booking and then I show the clients the providers websites and let him choose. Sometimes people advertise duos with other providers. I think it's also perfectly acceptable to email 2 companions together and ask them if they would be willing to do a duo together.
I don't have a duo section on my website personally because I'm still fairly new at doing duos, but I absolutely loved the experiences I've had so far even if I was shy at first.