Need some help with two goldfish that are sick!

Hi, I need urgent help with my son's 2 goldfish. Since Wednesday the one goldfish Ham started hovering in the corner near the bottom. Now today his aquarium mate Cheddar is also hovering next to him. Ham is most likely suffering from swim bladder, that much seems to be clear. We did try giving a pea but it didn't help.

Tank parameters are:
7.6 PH
High Range PH is somewhere between 7.4-8.0
0 ammonia
0 nitrite
nitrate at about 5 ppm
View pictures here:
https://imgur.com/gallery/ https://imgur.com/gallery/ozKYF https://imgur.com/gallery/agZfw (Test on the tap water)

The tank itself is 110 L (30 gallon). I'm not sure exactly how long he has had the tank. Roughly 3 months. Filter is an Eheim pickup 200 (2012) 220-570 l/h. There are 2 goldfish and both of them are small. They were bought from a pet store. He has had the fish for 2 months maybe? Nothing new has been added recently. He has done 2 buckets of water change in the past 2 days and another half yesterday night.

Here are two short videos to see the behavior.
https://www.youtube.com/watch?v=nrq3rOpEeWA&feature=youtu.be (Ham from Wednesday) https://www.youtube.com/watch?v=-hLtgM3JiYE&feature=youtu.be (This is with Cheddar and Ham together now)