The first one might be solid brass. The second looks electro plated and the third, less said the better... Test with a magnet and if you can get them off judge the weight.
Shame that someone has left those doors out in the rain. Even if they are beyond their original use the timber could still be of value. I got an old pine door on gumtree and used it to repair the paneling around a window.
Given where they are on the doors, they're almost certainly not original to them. Or, if they are, they've been moved. I wouldn't be thrown by the (modern) screws.
As with Fernicarry's post, I'd say top one: Maybe brass. Middle one: Looks like electroplated, I'd suggest modernish B&Q style. Bottom one: Chemically aged and laquered, available in B&Q style.
However, I guess the question is: Do you like them? Even if any are old, they're unlikely to be super valuable antiques. Even the one that is potentially older is an example of a design churned out in the millions. So, if you're thinking of salvage: Salvage what you like, not because they'll make you a millionaire