Ethen Pickett

Sounds like the charging flex you got is faulty which could cause all the issues you have detailed, I would try replacing it again and see if that solves them. If it doesn't fix the touch ID then check the home button flex cable as you may have damaged it when doing the original repair.

Yes you can replace the housing of the device but this will involve transferring over all the components into the new housing i.e Logic Board, Battery, Charging Port, Screen Ect. You can follow this guide here: iPhone 6 后盖更换

Check the logic board connector where the digitiser is connected and make sure there is no damage to the pins, also make sure you are connecting the digitiser connector correctly as this issue can happen when it is misaligned. If the board is fine and the screen is correctly connected then it is likely to be a faulty assembly, you'll need another to screen to confirm this.

Sounds like the new parts are faulty, either that or you are using the incorrect part. There are several different version of the Galaxy Devices so there are different charging ports depending on the model. The model of your device needs to match with the charging port i.e G935F model phone needs to be replaced with the G935F model charge port.

Could be an issue with the New Screen, if the cables are damaged of faulty then the home button just completely stops working even if everything else on the device is fine (found this out the hard way when removing a screen to do a new rear camera). Unfortunately you can't test this by trying a different home button to see if that also fails on that screen(which would be fairly cheap) because only the original button works in any capacity on the 7's so you'll probably need another screen to test.

Check that there is no damage to the pins on the screen and daughterboard connectors as they could have been damaged by the repair. If they have been you will need to replace either the screen or the daughterboard depending on which is damaged. Otherwise it is probably a faulty screen, you'll need to get a new one to test.

What quality screens did you get? Issues with the Touch ID are very common with the aftermarket screens so if you are buying aftermarket then they are probably just faulty screens

yes, it is a fairly simple repair, just one screw and a plastic piece to remove. Here is a good instructional video: https://www.youtube.com/watch?v=2ZEBtx2O...

You can check if the backlight has blown by shining a torch light on the screen, if there is no backlight then you'll be able to faintly see the screen when the light is shone on it. If the backlight is fine then its probably just a faulty screen, you'll need another screen to test and confirm.

Yeah sounds like the issue with her phone is on the board so a logic board transfer should work fine, best way to confirm is to go ahead with it and test it afterwards. It is a fairly straight forward process to swap the boards, just follow this guide here: Nexus 5 Motherboard Replacement