Will reference letters from a researcher who does not have a Ph.D be valid?
You can, of course, request a reference letter from anyone. However, the point of having a reference letter is to speak to your ability to succeed in a research program. Because a PhD is a marker of having succeeded in the same program they're recommending you for, it is highly recommended that you get a letter from someone with a PhD.
If these researchers know you well, then their letters can be valuable, but you should make sure to get a letter from someone with a PhD, if you can.