Window locks

Attached are 4 pictures of locks on my windows. I'm sending 4 so at least 1 of them might show you what I need. I am willing to change the locks altogether, if necessary, to make them actually work. As you can see (hopefully), they are supposed to attach to the windowsill, I guess, but that is nearly impossible. And I'm not sure that would make them secure, anyway. I purchased this house a few years ago, so haven't had working locks since. The locks have the name "Rusco" on them, and I presume they came on the windows, which appear to be retrofitted.

Do you have any suggestions?

Thank you,

Marilyn