You give hackers too much credit.
If you call the ISP they are not going to give you the IP address. They are going to tell you how to find it yourself, and they should be very suspect if you claim you can't find it.
Even with the IP address it does not allow access to your internal machines. You only have 1 IP address and both your machines share that IP, that is the purpose of the router. Your router is really stupid and since it does not know which of the 2 internal machines to send the so called hackers data to it will just discard it. People that want to run game servers in their house have to do all kinds of special setup in the router to make it actually send data to the server.
True DoS attacks just eat up your bandwidth they do not actually give the user access. Most of what you see in router logs is false, and is just hackers scanning for people who have misconfigured equipment. The log in the router means the router is stopping the traffic. It still uses your bandwidth but I doubt there is enough to actually affect your connection. Someone would have to pay to a service to do a true denial of service. Someone who tries to do it from their house would exceed their own upload bandwidth before they exceeded your download bandwidth.
If you actually think your PC are being accesses remotely there must be software installed on them. Try running malwarebytes first and then if you still think there is something format the drive and reinstall windows.
You should also make sure you have changed the default admin and wifi radio passwords on your router but in most cases these are printed on the router and even the ISP does not know them. You have to be able to look at the sticker on the box to know them.