OR, you can stop plastering photos of the guns on the internet and no one knows you have them! LOLSome very nice firearms, Joe! And at a great price to boot!
As far as firearms laws, tread carefully. I see you are from NY however am not sure if live in NYC. If yes, you will need to obtain a permit to take possession of those rifles and then will need to register them. If not, should be fine with long rifles and shotguns (barrels over 18 inches).
If you come across any handguns, you will need a permit and will have to register regardless of where in NY you live.
Before you go any further, I would suggest reading through the NRA-ILA's list of gun laws for your state. Below is the link:
NRA-ILA | New York
If there is any confusion, I would stop in a gun shop and ask them to help interpret the law. Do not, however, call a police station. They may ask you to immediately surrender them, especially if you live in NYC.
I'm not sure what the law is, however in PA, where I live, it isn't a requirement for a background check to be performed when transferring longs guns or rifles from person to person. If NY State is the same (if outside of NYC) then you have no issue.
A handgun on the other hand, a background check is a must. If you come across one, I would suggest going to an FFL (any gun shop) and asking them how to properly transfer ownership into your name. The muzzle loader in post 7 wouldn't apply as it would be classified as an antique firearm (it's probably a modern pistol, but because it does not fire rim-fire or conventional center fire ammo, it's exempt). You would however require a permit if you possess the components to make it able to be fired (powder, flint, percussion cap, etc.).
All that aside, keep us posted on what else you find!