Bottom teeth look always too long to the inexperienced! As I said, they are self-sharpening. if they have a nice even edge to them, then they are working perfectly fine.
Please make sure that your vet is NOT treating any front teeth on spec without the presence of premolar spurs, or she will inevitably make the problem worse instead of better! Sadly, dental treatment is not something that many vets, not even small animal experts, never mind general vets are experienced with.
Weight loss can have many reasons. If they are wheezing, then a respiratory infection is the most likely culprit. Loss of appetite and weight loss is typical for it, as the need to breathe comes before the need to drink comes before the need to eat.
Here is more information on the URI:
http://www.guinealynx.info/uri.html
If there is a URI, please ask your vet also for a diuretic to ease the build-up of fluids in the lungs, bisolvon powder to dissolve any build-up and overproduction of mucus. you can also place a bowl with hot water in which you put a few drops of olbas oil next to the cage.
Your vet should prescribe an antibiotic; make sure that it is given by syringe and not via the water bottle (which is totally ineffectual, as you cannot control the intake, especially not if the medication tastes horrible). If you are getting an antibiotic, please give a pinch of probiotic about 1-2 hours after the antibiotic to help prop up the guts and prevent further weight loss. Extra vitamin C to bolster the immune system can also help (about 1/8-1/4 of a human tablet).
http://www.guinealynx.info/uri.html
You may also consider hand feeding if your piggies continue to lose weight. More information on probiotics and vitamin C is included at the end. You will need to hand feed in case your piggies have any inappropriate dental treatment. If your vet is treating the teeth, please make sure that they get a painkiller like metacam.
http://www.theguineapigforum.co.uk/threads/complete-hand-feeding-guide.115359/