I only have a 17l with a goldfish and a shubunkin in it and a seperate 17l for water changes. I'm planning on a 125l in a few weeks as I want to build my community.
Many, many people have started out in the same way! Your fish definitely do need a bigger tank though; in the meantime, as many water changes as you can manage (at least 50%, three times a week, although more would be better) will help keep your fish healthy until you can get them a new home
Yeah, they get water changes often so no worries there
Have kept fish in the past and my mum has always had fish so I'm pretty confident, although looking through the forums I'm learning stuff I thought I already knew lol