The first thing you can do is take out the lizards.
Why would the frogs sit out in the open when possible predators are around??
I know people like to ad as mant different animals into one cage but it's not the best thing to do.
Int he wild it's different.
They aren't surrounded by glass.
The next thing you can do is don't plant your tank so heavy.
Have hide places but don't over plant and chances are you may see them more.
Lastly,
think about getting species that are bolder and not ones known to be shy.
I keep poison darts so I don't know about Mantellas but there are anumber of inexpensive darts that are known for being bold and sitting in the open..
My mint Terribillis and Centronells sit out all day long..