Simple way of telling the difference between the two frogs - clawed frogs have "fingers" on their front feet and bulgy eyes. Dwarf frogs have webbed front feet and eyes flat on their head.
Keep testing your water. With your results as bad as they are you need testing twice a day and probably doing twice daily water changes of about 80%. 10% here, 20% there won't do anything. If you don't do this, your fish will die. It's as simple as that. Change a LOT of water and re-test after an hour to make sure the levels are staying at zero. Don't post bad results here and ask if you need to change some water - any time ammonia or nitrite is above zero do a water change. There is no such thing as a non-toxic or safe level, as far as you are concerned (actually, there is a lot of tricky science in it but if you worry about that it'll just get more confusing).
2 small corys - need groups of 6 ideally, 4 as a compromise. Need about 50 litres minimum tank size
1 loach - will reach 6 inches, if not 8-10 inches, and will become very aggressive. Needs about 40 gallons.
2 Clown Loach - will reach 12 inches and needs 6 foot long tanks
4 Neon Tetra's (1 died) - needs groups of 6 and need 50 litres minimum (in my opinion)
2 Glo Lite Tetras (3 died over time)) - ditto for neons
1 Silver Shark - will reach 12 inches, need at least two buddies and needs 6 foot tanks a minimum
1 Male Guppy (3 died over time) - good choice for your tank
1 Tropical Frog - rehome if clawed as will kill your fish but good choice if dwarf. If a dwarf frog you'll need to feed bloodworms and other meaty foods by hand as they have got bad eyesight. Would like a buddy
1 Shrimp (1 died or was eaten) - good choice for your tank. Needs a larger group
5 Zebra Dinos - needs at least 60 litres
With a tank as small as yours (it's 30 litres, I just checked) you're looking at a very small number of small fish. In order to let you keep some of your stock you could try:
2 african dwarf frogs
6 shrimp (all same species)
5 male guppys
You ask why things have suddenly got bad? Stress and sickness related to bad water can build up slowly over time and can suddenly get triggered into sick and dead fish by something very small - like adding a new animal.
I'm sorry, but if you don't want to be cruel to those animals you need to rehome/sell/give the shop most of your stock. It's not a case of fussy internet people trying to spoil your fun (as many people seem to believe and as the shop will probably tell you). Most of those animals will become stressed, sick, stunted and end up dead before their time in your tank. The ones the survive will not be a testament of excellent fishkeeping or a sign that we are wrong - they will just be very lucky. Keeping even most of those fish would be like keeping 20 horses in a tiny townhouse garden and never letting them out for exercise and hardly ever cleaning them out.
I'm not meaning to be horrible to you - I think you have your pets' best interests at heart - but I do need you to appreciate the severity of the situation.