It seems to me that if you're measuring 100+ ohms into the sensor circuits that are supposed to have 90 ohms MAX and 45 ohms at half full, then something is adding resistance to the sensor circuits.

The only connection those two sensors share is ground or the selector switch. You've tested that the gauge response to correct resistance at the connector pin is correct, so that leaves the ground connection(s).

There are two wires from each sensor to a point near the selector solenoid. The 'hot' side goes to the solenoid and the grounds are connected to the frame somewhere near or behind the selector solenoid. If you lift the grounds and then measure the resistance between the hot and ground connections with the connector unplugged, you should see 45(ish) ohms. If they still read over 100 ohms, then each sensor has increased resistance somewhere between hot and ground connection which means you have to drop the tanks and inspect them.