Debra, It's normal for old or older leaves to yellow and fall off. If you don't see any spidermites on the underside of the yellowing leaves, don't worry about them.
It looks like your Chrissy came from below the original mother plant's "Y". She won't "Y" until she has completed her vegetative growth cycle. You can't force it.
Don't cut off that tuft on the 6' old stalk. I've noticed when the top is about to "Y", it puts out all kinds of little shoots near the top. If you don't want a standard that tall, you might try air layering a few feet below the top to reduce its height. Then you could cut off the leafless trunk leaving the new growth coming up from the ground. The air layered Chrissy would continue to grow and "Y", but as a shorter plant. The new growth look really healthy!
Gordo (Liz) has a thread on DG which shows how to air layer. The beauty of air layering is you don't interrupt much of its growth. In 2 months, you would have a shorter Chrissy ready to pot up or plant in the ground.
