1. Did I overwater the plants? (I believe I probably did)
Hard to say, each place and situation is uniquely different.

2. Will the leaves coming out at the lower level continue
to be the growing plant?
No, all the new leaves that you see in plants like bananas and palms are formed from the center. Since you said the center of your bananas are rotted, the outside leaves will continue to grow until they die then the plant will eventually die.

3. If so, should I cut the stalk down to the level of
these leaves, or should I just leave the stalk? It
appears to be rotted in that part.
Gradually cut down the stalk until you see no more rot in the middle..

4. Is there anything else I can do to help these plants?
Sunlight, fertilize, water and be sure to amend the soil..

5. Since the soil contains clay, would watering a couple
times per week be sufficient even in 90 degrees plus
temperatures?
See answer the number 4.

Thanks - appreciate the input.

I am not clear about what you mean when you say two of your plants "have sprouted leaves about 4 feet up on the side of each stalk. These leaves are under the original top of the growing stalk, and are now appearing to grow, even though not out the top of the plant."
Would it be possible for you to post a picture of this?
Pat

The URL shows three pictures of the two banana plants in question. The leaves that you see in the pictures sprouted about 20" from the original top of the plant through the side of the stalk. (I cut the original tops off as they appeared rotted inside) They now appear to be recovering - can you determine anything from the pictures? Appreciate your help.

Here is a link that might be useful: JohnBurns Banana Plants Pictures

This is apparently a common occurrence. I had this same thing happen this year on 2 of my Namwa plants and also on my Ice Cream plant in the ground this year and when it was potted last year. My Ice Cream had to be cut down to about a foot tall from about 10 feet tall before winter hit. I have heard that the cause is water sitting in the unfurled leaf for extended periods of time due the lack of growth that winter brings. Once the healthy unrotted portion inside the P-stem starts growing again in the spring it pushes it way right out the side of the p-stem. In time all the old top growth dies off leaving just the new growth which becomes the new top growth.. On a recent visit to Pitangadiego's place he told me he has experienced the same problem. I can post pictures if you need.

Thanks for your post, momo1 - it reassures me that my plants will probably recover - which they seem to be doing already. It's not necessary to post pics, but I do appreciate your reply. Thanks.