OK, I will go by the pics I see on photobucket since I don't see the Ariel pin you are wondering about.
1. What I think is the backside of a Lion King pin - I believe pinpics #2436. As this is a very old pin, and considering its origins, I believe yours to be real; this specific pin has never come into question before and it was made waaaaaay before people started making fakes. Fakes were made at the time of pins that were current at the time of production, and since your pin is so much older than any fake, I would say with 99.9999999% certainty that it is fine.
2. Dalmatians pin - 100% guarantee it is fake. These were faked a LOT. Your pin has rough edges, the hidden mickey icon looks terribly disproportionate, and perdita's pupils are completely white where there should be black.
3. Dale - Hard to tell from your pic. Would have to see the back as well. From the front it looks good -but- they did fake these a lot since they are easy (black and white/greyscale). Would say from front pic about 75% certain it is real.
4. Round Pooh - 100% fake. These were faked a LOT. There is extra metal on the side and the lines are too thick.
5. Nemo set - Unfortunately, you happened to collect an entire set of fakes. The real ones (in my collection) had white bag tops, not yellow. All the fakes were yellow topped like yours. That and add the fact that a lot of the fish look rather sick from having colors that are off or completely wrong; 100% fake.
I am really sorry to have to break to you the bad news but I really do hope that I helped and that hopefully you can start down the road to learn the difference in order to protect yourself.
Good luck collecting!!!