You need to at least mix that soil with at least 50% perlite. Pull the brown one out and check the roots. Cut off brown parts till you see green healthy tissue clean in the blade in alcohol Inbetween cuts hope this helps. :)

The pieces that are turning brownish, reddish are they still firm or squishy? If they're firm you should wait to cut until someone else gives advice bcuz the color could be changing due to weather etc. but if swishy I would think rot would be the culprit then you would want to cut. But I would definatley still add the perlite.

Normally with vegetative propagation of succulents you let the cuttings etc. air dry for awhile before inserting them in moist soil. If these didn't come off with roots, did have exposed cut surfaces the one is probably rotting.

I had my Aloe vera in a grittier mix than you have. In SW Florida I need excellent drainage to get through the summers.

That being said - here is a picture of 2 plants that I had in pots sitting next to each other in full sun. One was nice and green and the other was brown, just like yours. I found no problems with the roots on the brown one. It was firm, just brown.

Both are in the ground now and both are nice and green and producing my first pups!

I have two that looked the same orangey brown most of this summer. Mine was caused by too much sun. But two days of cloudy rainstorms gave it a chance to bounce back and is a healthy green again (some outer leaves still look a little tan). If it's not rot, perhaps give it some shade for a few days to see if they sun is the problem.

Now we have a bigger problem. The outer leaves are getting squishy and turning shades of brown to dark green. Are they rotting? It's getting low as 18-30 F in my area. Should I bring them inside?

Whoa - this plant is not cold-hardy. I'm hopeful you haven't killed it, but consecutive freezes will do just that.