They are compatible, but it is changed to APS-C mode (factor x1.5). The 11-18mm lens also fits between 12-17mm in full frame mode.

Only full-frame lenses are compatible. Either E-mount full-frame or with adapter A-mount full-frame lenses. For dt lenses (APS-C) A-Mount or E-Mount the resolution is automatically reduced to the APS-C format (if set in the menu) 10 Mp.

No, not directly.
The Sony A7 series are compatible with Sony FE (E-mount) lenses. It must be ensured that these are suitable for full format (otherwise you can only take photos in APSC mode, i.e. with lower resolution).
A-mount lenses (also make sure they are full-frame compatible!) are compatible with the 'LA-EA3' adapter (https://www.digitec.ch/de/s1/product/sony-la-ea3-objektiv-adapter-objektivadapter-2441581).