These are mine! What has happened? I don't even remember the names of these beasts! Yes, I know I've got the light and water wrong. Help me help these guys please!!
Could be Ceropegia on the right. Would you be able to add a closer pic of the one on the left? Does it have 'regular' or succulent leaves?
The one on the left is a pilea; photo here any better?
What's happened is this: The plants are trying to deal with cultural conditions at the extremes of what they are genetically capable of dealing with. This causes stress, then strain, and strain uncorrected always leads to the death of the organism. To turn the decline around, you'll need to identify the cultural conditions that are limiting and correct them, or find a way to press the reset button.
I'll link you to a thread you should find helpful (below this post). If you have any questions, ask here or there - whatever you prefer. Tiffany (purpleinopp) will also have good advice for you if/when she visits the thread again.
Here is a link that might be useful: About that reset button ......