If this is the only shower you will have, then just invite them all. But if there will be one in either your of DH's hometowns or hosted by a family member, you would want to invite family to those. It might be just me, but I think the exception to that rule is the future grandmas, they might want to be invited to all showers.
As for the venue, it wouldn't hurt to ask. When you get back to her with some date/time just ask her if she knows where she is holding it.