Hi there! Sand is okay for them once they get around 6" or so (in my opinion).. .5 - 1mm grain sand is what should be used. Most of the time the axie will spit out the sand they suck up.. But you want to be safe, especially when they are little!
Honestly I wouldn't worry about cannibalism. Just feed them lots when they are little, they will grow fast and grow out of that stage pretty quick as well. I think 20G is alright for two. I have three axies at about 3" right now, got them when they were 1.5".. They were raised in large groups under close watch and the owner had no missing limbs or gills, neither have I. (Obviously that is only two cases. I'm sure it depends on the axolotls individually) But 20G is enough space for two babies (assuming you are getting small ones?) I doubt they would bother biting each other.
I would recommend you check out
www.caudata.org it is a forum site with a lot of axolotl people! They can answer everything for you! You will find a lot more information there.
Axolotl's like little to no lighting on their tanks, caves and tunnels, and cold water. They don't like water flow.. A lot of people don't use filters on their axie tanks. Just do a lot of water changes to keep it clean. I use a filter, i just keep it on the lowest setting and I have plants in the way of the water flow part to make less of a current. They don't need a lot of oxygen in the water so bubblers are not necessary.
You will find a lot of contradicting information on the net, just do whatever works for you! If your pets are happy and healthy then that's all that matters. I hope you get axolotls! They are really cool and very unique!
what is the temperature in he tank you plan to use? Don't get two babies unless you have two tanks, as they are very cannabalistic until about 4" length.
