Guppy Tail Was Eaten

[Punk213k]

 Hello.. about a month ago i added my fully grown crawfish in my 55g fish tank with the rest of my fishes.. the next morning i notice my orange guppy had been swimming alone for awhile and when i took a closer look my yellow guppy had half his tail cut off over the weeks i have notice its tail has started growing back my qustions are
1. Will my yellow guppys tail fully heal?
2.Is 10g tank 2 small for my fully grown crawfish? All it does is hide in his cave until feeding tims pretty much.

3. My crawfish is missing one of his claws i have heard they grown back with each molt but mine has not molt since i got him like 6-7 months now guessing might be 2 old
4. I still have yet to identfy one of my fishes i bought him to keep my white widow tetra company while a searched for more of its kind its orange triangle shaped 

 

 

[Lillefishy]

If it's only the fin of the tail that's gone & it hasn't affected the body of the fish then it should grow back.
You have an incompatible mix of fish in your tank, Bettas don't as a rule get along with guppies & could be the nipping culprit.
The triangle fish you mention is an albino tiger barb, they should be kept in groups of at least 6, they are notorious fin nippers when kept in small numbers so he could also be the culprit, imo tiger barbs should be kept in species only tanks
I would move the crawfish out, it's not usually a good idea to keep them with fish.