Bigger tank is always better! But really, a 20 will be fine for now, you just have to keep up with extra water changes. When you can no longer manage water quality with weekly pwc's, it is time to trade up. <Some people do keep goldfish is smaller than ideal setup, but to keep the fish healthy, they have to do daily pwc .... that is too much work for me!>
BTW - I would try to trade up to a 40 or 50 breeder .... You actually want to have goldfish tank with bigger footprint so there is more surface area for gas exchange, and the shallower breeder tanks are ideal. I don't think it is worthwhile trading up to a deeper tank (like the 29), you are not getting much benefit.
As for if the fish are healthy - nothing obvious on the pic, but behavior is much better indication than static pics. healthy goldfish should:
1. Hold their fins out, with dorsals mostly erect.
2. Be always active unless sleeping. Goldies should spend most of their waking hours booking (nosing around the gravel looking for food).
3. Eat like a pig, all the time!
4. Have no visible poop. <No long strings of poop hanging out the backside, not a lot of poop visible on the gravel ... healthy goldfish poop breaks down quite quickly.>
5. Have bright eyes & clear slime coat.
6. Have no obvious buoyancy problems. Fish should not be struggling (or expend much effort) to stay either at the surface or at the bottom.