How to protect Microcontroller from any damage if there is motors and sensors on PCB
You should not need to opto-isolate digital lines that are operating in the right voltage range. The CC1350 should only operate up to 3.8V so you need to make sure to run all the other logic at an appropriate level or use level shifting. Pins are tolerant to VDD+0.3V
Put bidirectional TVS diodes across the motors to protect your circuit from back-EMF. Pick a breakdown voltage above the applied voltage (~26V) and below the maximum voltage of the motor controller (45V in your case). I would recommend a minimum breakdown around 29V so your maximum clamping voltage will still be below 45V.
You state that your motor voltage is 24V but your battery is 25.9V. Don't try to regulate that down. Since you are using a current controlled motor driver, the voltage is not so important. You can apply 25.9V directly to the VM on your motor controller.
If your sensors output voltages higher than the VDD on your MCU, scaling with resistors should be adequate.
Grounds do not need to be isolated but you do want to pay attention to the return path through the PCB. You do not want large currents being forced through the ground plane under the logic level components.
If you do decide to run isolated, tie the grounds together with a 1 MOhm resistor. This will keep your isolated circuit from floating to arbitrary voltages that may exceed the breakdown voltage of an important component.