The first picture could be fin rot but it's not infected with bacteria so that's good.
Second picture, the orange guppy looks like someone has been biting pieces out of the tail. It's not infected with bacteria either.
The black and blue guppy under the orange guppy looks like it has a milky white edge to the tail. This is excess mucous normally caused by low pH or poor water quality (ammonia, nitrite or nitrate).
Third picture, the fish looks like it has little bites in its tail. Again, it's not infected with bacteria so that's fine.
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What other fish are in the tank?
What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
What are the ammonia, nitrite and nitrate levels in the tank water?
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You can add some salt (see directions below). You can use salt and dewormers at the same time but I would wait until after you have finished treating the fish for worms before adding salt, otherwise you will need a heap of salt.
If the fins start getting red lines in them, or they get red patches/ areas on the body or fins, post pictures immediately because that is bacteria infecting them. But for the time being, just treat the worms and then worry about this later.
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Make sure the pH is above 7.0 and the GH around 200ppm. Again though, if the GH is too low, wait until after you finish deworming then buffer it.
If the pH is too low, you can add some limestone, dead coral rubble or shells to the tank or filter and they will help buffer the pH up.
