Getting them mixed up is easy to do - especially when there are so many of them! The "tree" just keep spreading out and out and after a while it's hard to remember who is related to who and how!
I haven't come across a Samuel Heth or a Gertrude Kelly or a Samuel Raymond Heth. Heth is not a very usual name, so if you keep looking, I know you will find them. Sometimes the name is spelled Heath (one marriage record I found in my family had "Heath" but everywhere else it is "Heth". If you go back far enough sometimes the name is spelled "Hoeth". I've traced my line back to Pennsylvania via the census images on Ancestry.com. If you haven't checked them out yet and can afford to do so it is an excellent resource.