Without being rude my first recommendation would be throw the model away and start again. Unfortunately it is a rats nest of loose , stray and hidden geometry that is mostly out of alignment and on mixed layers/tags.
If you look at this gif you can see all the hidden geometry that will drive you to insanity.
I would start from Scratch. Turn off length snapping as mentioned above and set that, with any other style changes you might want, as your template so it is always off.
Then draw your model using mostly the rectangle tool so things tend to stay flat and ‘group early and often’. Meaning make groups and components of everything as you go so things don’t stick together and effect everything around them. 'accidentally shift one corner vertex and the whole house is suddenly out of whack.
Leave Untagged as the active Tag and only assign a tag to groups or components, never loose geometry. If you explode a group/component that you have already tagged reset that exploded geometry to Untagged.
Work in monochrome mode so you can keep the face orientation corrected, all white faces should be visible, blue are back faces and should be contained within shapes, unless it is a single skin. But then nothing in a house would normally be a single skin as it has no thickness.
Keep the original model if you want as a reference, but have it open as a second instance of Sketchup and build the new one in a fresh clean instance.