Dad is better but still feeling weak. He and Mom seem to be doing OK at home.

Dad is likely weak because of the cancer, not because of poor nutrition, according to his cancer doctor.
After a day of riding and walking into doctor appointments, he did not feel up to trying to drive.  At first he had thought he would try it again, but decided against it.
Dad commented that he is not used to getting winded so easily.

At the urologist, it was explained that if the chemotherapy eliminates the liver cancer, and reduces the bladder cancer, then only a portion of the bladder can be removed to get the rest of the cancer.
It will be quite a few months before the results of chemotherapy will be found out.
While riding along in the car, Mom got lost, and asked the road name.  That gave the chance to explain to her that she had known the name of the road just a couple minutes ago, and she had forgotten.  It was then explained that Dad worried about her driving because she might forget where she is and she gets easily flustered,  She seemed to understand, and later in the same trip said that she is not really fond of the idea of driving anymore.  (However, I am not overly optimistic that she will in the future understand nor remember why Dad does not want her to drive.)

Dad is glad he is much healthier than he was recently.
My parents are still not infrequently bickering, but also seem more frequently trying their best to be kind to each other.