D.B.
I think it's refreshing that 2 adults with a family and 14 years of history are doing this on their own. I think you should congratulate yourselves on raising an independent daughter who waited until the time was right to get married, and who did not impose any of this on you.
It would be inappropriate for parents' names to be on the invitations if it's not your party. I do think it's unusual that they have not asked you for the names of close friends or relatives who might like to witness this, but then again, they've been together a long time so maybe they think either it would look like a gift-grab or it would be an expense for them to include your friends. Maybe they ARE inviting some of those people and they just haven't told you, because they want to do it themselves and they know how to get hold of people who are important to them.
I think a lot depends on how you know the bills are coming in. Are they moaning and wringing their hands, wondering how to pay off these expenses while still making the mortgage and paying for kids' shoes? Or are you just overhearing her tell him, "Hey, the caterer wants a deposit by Friday"? The first means they overspent or they are hinting; the second means they aren't hiding from you.
I'm not sure what your relationship is with her re financial matters, and whether you can talk openly or it's an area of conflict where you have perhaps disapproved of her decisions in the past. If you're open, you can just ask. But it doesn't sound like that. So, if you have argued about this in the past or if you think she's been extravagant and now is expecting a bailout, be careful getting into that. If you don't want to be asked to cover a deficit of unknown proportions, you might decide on a specific amount and ask if she'd like a check for X now, a wedding gift (I don't know if they have a registry or if you have a family heirloom to hand down), or if she'd like it put into a college fund for the kids. What I would not do is leave it open ended - if you have $1000 in mind but think she might ask for $10,000 if you say just "I'd like to help since it's so expensive," you could get in over your head and wind up with hard feelings.