Can you post photos? Post photos that allow us to see the whole plants and also some close-ups of the dying parts. (Leaves? Are the stems healthy? Is fruit affected?)

Also, we need know something about your growing conditions. Where are you located? What are they growing in (ground? raised beds? containers?) What kind of soil/container mix? How often do you water and how? How often do you feed and with what? How has your weather been since you noticed the problem?

Also, the title of the thread should be the topic, not your name. You will get more responses. Once a tomato starts bearing fruit, it's normal for the lower branches to start yellowing.