I agree with Mush here, the betta is still safer by himself, and the newt is not a suitable tank mate if this is the tank we're speaking of:
10 gallon tank
3 Male plattys
3 Female Plattys
1 Common GoldFish
1 Fancy GoldFish
1 Japanese Newt
Newts also need tight covers, they like to climb out of tanks, and once they dry out, they're done for. Newts also need dry land to roam around on, higher humidity levels above water, proper lighting, and lots of decorations to hide in. Newts need a vivarium setup, and if kept in a fully submerged environment for too long, will die.
The goldfish also should have a much larger tank. That fish will grow to approimately 8 inches, and they are one of the dirtiest fish around. Bettas will eventaully chew apart the fins on fancy goldfish, which, in turn leaves the goldfish open to infection and many other issues. The common goldfish (comet) should also have a very large tank, and I don't suggest keeping them with fancy goldfish because they tend to bully the fancy goldfish as they get older and bigger. Comets grow to 14 inches long, and also are extremely messy and dirty. Both goldfish will need plenty of extra oxygen in their tank, as they are high consumers of oxygen compared to the typical "tropical" fish. The other reason for seperating the goldfish is because they are cold water fish, and should be kept at 65 - 68 degrees. The other fish are tropical fish, which means warm water (mid 70's - low 80's). The warmer the water the lower the oxygen content.
This is the time to sort them out, before there are problems. Goldfish tend to grow very very fast... from 2 inches to 6 inches inside of 6 - 8 months is typical for the comet, a bit slower for the fancy goldfish, but not much.