First of all, welcome to AA. You will find many people here who are happy to help you.
That being said, please don't take this the wrong way, I'm only trying to help.
First of all, a 5 gallon is way too small for even one clown to survive for any period, not to mention 2. Don't know which kind of clowns you have, but most get to be 3-4 inches. The ammonia build up will eventually kill them if the ich doesn't.
You say the aquarium was purchased last weekend? If this is the case I'm sure it did not properly cycle.
I would suggest calling the fish store and ask if you can return them until you can provide a proper setup for them. I also would suggest reading through this forum and looking at posts in the "getting started" forum. These is a world of info there on setting up a system.
If your fish store will not take them back or you simply don't want to, I would suggest turning your 5 gallon into a hospital tank and treating them for ich. (much info in this forum about a hospital tank and ich treatment). At the same time you could get a larger (30 gallon or so) system for them and do a proper cycle and setup. Once the treatment is done, your new tank could be ready for them. I'm sure you could provide a great home for them is an appropriate size tank.
Once again, not trying to offend, just trying to help. Please let us know if you have specific questions. Your fish are not doomed, if you take appropriate actions.....soon.