After spending best part of £100 on plants, you can imagine my frustration at seeing lots of leaves half eaten. I think it might be the Mollys. I was told assassin snails don't eat live plants, is this correct?
Your plants might just be transitioning from emersed grown to submersed growth. Even plants that have been submersed prior to adding them to my tank have gone through lengthy transitions due to the change in water from one tank to another. I've never had mollies so I can't tell you if they eat plants or not though. Also, I could be wrong but the plant you have all the way to the left that looks marbled is probably not a true aquatic. I also have doubts about the one all the way to the right that looks similar to a fern. They remind me of plants I've seen at Petco in tubes that they try to pass off as aquatics. I learned that the hard way myself. They look like very nice Terrarium plants though!
And the taller plant on the far right looks like a Chamaedorea elegans seedling, a very nice palm house plant.
I would pull those non aquatics out and take them back to the store to get your money back especially if somebody at the store 'helped' you pick them out. If that isn't possible get a decorative shallow pot and make up a house plant arrangement with them. They are nice plants but won't do well underwater for long. I would get your money back if possible, likely you paid a lot more for them as aquarium plants than you would have as house plants!