25 g tank problem

Hi! My name is(what) my name is(who) my name is Cacret! Currently i have a 25gallon aquarium that I intent to make into a reef tank. It has a hanging external filter, white and blue led light, 3 kilograms of live rock, and I have been cycling the past week. I ran into a problem though, 3 days ago my grandfather gave me 3 clownfish and 1 damsel, even tho I intended to wait till the corals are settled before adding a lot of fish(i wanted to let the corals go first then only have reef cleaners and a pair of clownfish until the corals are complete). I dont even have a water tester kit yet! All I have is a hydrometer. Anyways I felt that with 4 days of cycling it would be fine. The two clownfish have died and while the one is left is doing pretty well, I wouldnt count on it looking fine because the 2nd to die came out of nowhere. The damselfish however has been brething rapidly(do I need an air stone?) The salinity is 0.4 too high than what i read is recommended for fish in general.(I read that 1.19-1.25 is recommended). Temperature is probably too high(29°C) so what do I need? Well I Have a lot of questions of about the parameters, fishes themselves and other things.

Question 1:
Arent clownfish(ocellaris) hardy? I read they are really good beginner fish because of how hardy they are. However this appears to not be the case. Are clownfish truly hardier than what I said.

Q2:
Why is my damsel breathing rapidly? My forst clown that died was breathing rapidly before his death but the damsel was like that since day one and hasnt died. He usually stays at the side near the filter where the water goes back in the tank(bubbles?)

Q3:
Is RO/DI filtered water really necessary as the water to mix with salt? I used normal tap water but I read its bad. I assumed after a lot of cycling it would be "purified"(especially since my filter supposedly has good bacteria).I have used tap for a long time as the water for my freshwater but, is it different?

Q4:
What would you(an experienced keeper or someone with experience) recommend as salinity for :
-Ocellaris clownfish
-damselfish in general
-gobies in general
-hermit crabs
-banded shrimp
-firefish
-Zoonthid corals
-anemones

Q5:
What should I do now? I have a not fully cycled tank and two inhabitants in horrid conditions. Should I do water change? Do I need to buy:
-RO/DI system
What do you recommend I need to get?

Anyways I hope thos wasnt TL;DR
Thanks for your time!