Help treating 2 cute dogs from tick

I was taking my family to a pet store. And I found 2 cute dogs. (brother and sister) i took the youngest (the girl) to home. I found out thay shw is full of ticks and scratch a lot. I couldn't take this so I thought thay I go back to the store and ask them to treat her. They said thay they can not and now it is my problem and I have to deal With it. I ask if the bky have the same problem they said yes. So I bought the other dog (the boy) and I decided thay I will try to treat them both (the brother and sister) after seeing how they abuse their peta and not caring for them. I need help With The medication and toola thay arw needed to solve this problem.

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