Hi madogz77, and welcome to Loaches Online.
Have you had a read of our clown loach info on the main site? If not, here are a couple of articles to get you started:
http://www.loaches.com/species-index/cl ... cracanthus
http://www.loaches.com/articles/an-intr ... ping-botia
Did the tank come with any additional filtration other than the built-in Juwel filter? The Juwel filters are not very efficient and the loaches would benefit from additional filtration and water movement.
I would also look at changing that sharp-looking gravel for either aquatic sand or smooth fine gravel. That white gravel looks quite rough and it could cause damage to the loaches delicate sensory barbels.
If you have fallen in love with the loaches, be prepared to change things to meet their needs - this also means upgrading to a much larger tank in the next few years. You'll also need to add more clowns (at least another 3, after quarantining them) to bring the shoal up to at least 5 in total. They are incredibly social fish and although two may seem happy, they will not be able to behave all that naturally.
You may also want to trade in the mollies at some point, as they prefer much harder, alkaline water compared to that of the loaches.
Clown loaches are too often sold for tanks that are too small for them and they become stunted, never reaching their full potential (this will also have health implications for them). It is hard to estimate how long it would take them to reach full size, but I would guess 15-20 years if kept in good conditions from the start. They are known to live for over 40 years, so are a long-term commitment.
Good luck, I hope this helps.
Emma