Is this size difference harmful to my tankmates?

I finally got my 20L completely set up and cycled, and added my new friends from the Model Axolotl. I'm using Carib Sea "super naturals" very fine sand with some large aquarium stones, two terracotta pots and two pvc pipe joints with plenty of plants.

Nitrates/nitrites 0, ammonia 0 and pH is 8, tank temp a steady 68. The lotls themselves are beautiful and healthy, Dionysus being about 5 1/2" and Demeter being just over 5".

They haven't been interested in eating more than 1/2 a worm each but I did see Dionysus nip at Demeter's tail once and it occurred to me he seems so much bigger than she. They aren't too much different length wise, but I noticed Dionysus is a lot thicker than her - he's almost a solid 1/4" wider. I couldn't get an image from the top because my phone wouldn't focus but hopefully you can tell he's a good bit wider than she is from this picture.



Is this something I should just keep an eye on - feed them separately and make sure Demeter catches up a bit? - or should I take a little more extreme step and keep Demeter in another tank until they're both a little more mature? I believe they're nearing 6 months old.

*Please note the display light was only on for the purpose of pictures.
**I'm sorry for the massive amount of probably unnecessary information, these aren't my first axolotls but this is the first time I've had this issue and I don't know which route to take.

As adults I keep axolotls together which are up to 25% smaller lengthwise, I'm not concerned about body mass differences as females can get a lot bigger when they are gravid. Size differences in juveniles can be more problematical, I have seen them eat tankmates up to 75% their own size. Yours don't seem excessively different lengthwise but you may encounter problems for two reasons, firstly if they are from the same batch one is growing faster than the other, this size difference due to growth rate can increase fast. Secondly if the bigger one bites a limb off the smaller one its growth will be retarded increasing the size difference over time. Atm I wouldn't bother separating them but if the size difference increases I would consider it, you can reduce the likelihood of a missing limb by ensuring they are both well fed and to prevent accidental biting feed them at separate ends of the tank.