The other question to ask yourself before you buy anything is what will you do at the moment that your security camera captures something? Will you be home to do something immediately?
When someone knows that a security camera is there and they have access to the house, they are often a lot of ways to get around being identified.
What happens if you’re away from home and your home office camera detects movement and then shows you this:
Will you be any better off than not having a camera at all?
That’s why the question of who you think you’re trying to catch also matters.
A hidden camera, like a nanny cam, will only be legal for some people and some parts of the home, depending on the state where you live. But even so, say you catch a teen stealing from your office once. Once they know the camera’s there, it may not be a deterrent.
I’m not saying don’t get cameras, particularly exterior cameras. They can be a very valuable family security tool.
But if your issue is with people that you know who have permission to be in the house, interior security cameras are only one step in treating the problem. You need to think about both the steps to come before and steps to come after The camera catches the image. And when it’s a frequent and prolonged problem, like you’ve described, you’re not looking to just solve a one time event, and that makes everything much more complicated.
So just some more things to think about. 
I am myself a medically fragile person and have home health aides. I also have two roommates and we all have friends and family, so we have a lot of people coming through the house. We did have a problem with theft at one point, so you absolutely have my sympathy – – I know how frustrating and annoying it can be. Our circle of suspects was pretty small: One crazy girlfriend (not mine!) And one of the new health aides. Our goal was mostly to clear the innocent person, to be honest. But we only needed to catch the person once as neither of those two people lived in the house, although both sometimes stayed overnight. We just needed to know who it was so we could then take the next steps. So we took steps, found out who it was, and then just barred that person from the house. But that’s a whole different situation than when the person lives there. 
You can still use interior cameras, but you might use them in a different way. There are cameras for example, that can do facial recognition, like the Netatmo.
If one of your kids has a dodgy friend and you have told your kid not to let that friend come to the house, and you use the facial recognition for things which the kids like to have happen when they get home, then you could get an alert if they did have the dodgy friend come over. That could be useful.
But if you have a persistent problem with someone who lives in the house, it’s a whole different kind of issue, and the camera will only end up being one very small part of what you have to do to solve the problem.
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