I’m concerned about this but is the family allowed to have multiple cameras that video and audio while I’m at their house?

I run a babysitting agency (and work at a Memory Care community part time as a receptionist). Lots of our clients have nanny-cams in their homes in order to observe their children AND the babysitters who sit for them. It's their prerogative, their right, their home. They do let the sitters know ahead of time, so it's the sitters right to take the job or refuse it. If a sitter likes to play on her phone all day, she's likely going to have a problem with a nanny cam. If she's going to devote her time & attention to the children, she's not likely to have an issue with it.

Laws vary from state to state. You might want to find out what the laws are in your state. In my state, it is illegal to record (and I am assuming film) anyone without prior notification.

To look on the bright side: as you're caring for a person with dementia, the day may dawn when you will be very glad the cameras are there! They will provide evidence that you did not do the wicked things your client might take it into her head to allege :)

Provided you have been told about the surveillance, and the cameras have been installed with the consent of the homeowner and/or the homeowner's POA or guardian, there is nothing wrong here. I can imagine it feels a little uncomfortable at first, to be monitored all the time, but I'd expect that in a while you'll forget all about them.

Are you otherwise happy working with this family?

The cameras are legal. You have no rights in regard to this. It’s a private home. As long as they aren’t recording you going to the bathroom, there’s no wrongdoing here.

I am almost certain that cameras on your own property are legal. I have gone from anti to being an advocate in my own city. I assume at all times that there is a camera on me when I pet sit, when I walk my dog and pass a lovely succulent "pup" (a tiny baby growing off a succulent plant). The truth is that they keep us on the straight and narrow and often in my city catch those who are breaking car windows, stealing packages, and abusing animals or people. In the UK they are common on the streets everywhere and help enormously with criminal apprehension. I used to be such a proponent of our privacy rights, but after 9/11 they are a thing of the past anyway. Always assume that everything you type into your computer is captured in a law office, every single word on your phone, said or texted, is public domain, and every where you move, if you have a cell phone, they know where you are. A friend recently won a 100,000 suit for defamation from a Facebook scribbler who said bad things about him, and he got access to every word of her conversations on FB even in a private group conversation.
When in someone else's house, I am afraid those good old days of going through their medicine cabinet just for fun are over! Move in the world as though the camera can see you every second. Does make you think twice in the bathroom I guess, but there you are.

If it's a private residence I would think they can do whatever they like. They are just looking out for their loved one.

Perhaps check with your employer, though, and find out what your rights are (if any) to reasonable privacy when working with a client in their home.