Could political will have completed the G3s?

Would sufficient political will have allowed Britain to complete Hood's sisters or the G3 battlecruisers?

Yes. Britain could have completed the G3s, but doing so would have forced a different Washington treaty negotiation.

The Royal Navy could have completed the G3 battlecruisers if the British government had insisted. That decision would have changed the treaty bargain rather than merely ignored it. Britain could have demanded that the ships be accepted within the agreement, using withdrawal as leverage much as Hood's status was accommodated. Warship construction depended on political commitment and diplomatic bargaining as much as technical readiness.