What are these Generic Windows PC / laptops connecting to my network at night

Your post with that pic with the two MAC addresses was marked as "Private" by the forum bot. They are considered to be personal information. The posting of personally identifiable information is a violation of their forum guidelines. Please delete that pic and repost it with the MAC addresses blotted out if you wish. The bot will not allow your post to be seen publicly.

That said. Are you using a Comcast rented gateway device ? If so, check to see if the MoCA feature is enabled. Perhaps your neighbors are inadvertently connecting to your network / gateway device with it. MoCA (Multimedia Over Coax Alliance) is an alternate hardwired way to connect devices to a home network if ethernet cabling can not be used/run. It uses the existing coax cable wiring instead of ethernet cabling.  If the MoCA feature is enabled, and you do not have a PoE (Point of Entry) MoCA filter installed on the coax line, yours, and your neighbor's gateway devices will be able to connect with each other like one big network. 

Disable it if you aren't using it. If you are, install a PoE MoCA filter on the input port of the first splitter off of the street coax drop to keep the MoCA signal in your premises and to keep the neighbor's signals out. Your neighbors should also have PoE filters installed. To disable MoCA on your device. First, unplug the coax cable line from the jack on the gateway device. Then go to the gateway login http://10.0.0.1    

Default login info is:
Username: admin (all lowercase)
Password: password

Once in you will find the drop-down on the left of the screen that is labeled “Connections”.

Click the drop down---> click MoCA---> right side of screen click “disable”---> save changes.

Bear in mind that we've seen many posts here that the MoCA feature gets turned back on with their overnight re-boots / updates for the device. The best policy is to be sure to use that PoE filter ! Amazon has them: https://www.amazon.com/SNLP-1GCW-Filter-Eliminate-Multi-Room-Interference/dp/B07SLD9QPH     

Or you may be able to get one for free at your local Comcast / Xfinity store. Or book a tech to come out and install one for you.

If the MoCA feature is not being used on your home network, you can put the PoE filter right at the back of your gateway device instead.

@user_r4feuy 

Thanks for editing out the personal info in your post. It is now publicly viewable. Did you have a chance to determine if the MoCA feature is the culprit ?