No your Betta splendins (Siamese fighting fish) isn't happy in that 12 oz. glass
Yes that gold fish could have lived many years BUT NOT IN THAT BOWL
No you can't keep 30 fish in your 3 gallon tank just because of the picture on the box
Yes Angel fish are Cichlids
No you can't keep Oscars in your 10 gallon tank
Yes you have to do water changes
If you can't find the arowana look on the floor

Yes I know the person at the shop told you they would get along. BUT.....

No you can't keep guppies with a red tailed cat

YES you STILL have to do water changes