I would lean towards it being a bacterial issue and not allelopathy. I have combined Colorado, Sunbursts, Mak Infernos, Supernovas, Infernos, and Lemondrops over a 1-2 year period. Each started with a pre-emptive cipro treatment before being added to the system. I had success with it but I think other factors besides the cipro treatments were helpful in my setup for it to be possible.
1) I run UV 24/7
2) I had a decent amount of total water volume... 320 gallons. I would not try this on a smaller system.
3) Some of the anemones were physically in another tank that was plumbed together though they did share the same water
4) ran ROX carbon 24/7
Some observations down the line as I slowly decided to narrow down the anemones I had. I only kept Supernovas and CSBs moving forward.
1) It works until it doesn't work. Even just moving an anemone from one tank to another in the same water could cause issues.
2) Adding back in clones from my own CSBs that spent 2 years in another person's system with no other anemones caused mixing issues. So full genetic clones reacted in the tank as if they were foreign when reintroduced and caused some anemones to react and start declining and losing color.
I have no experience with mixing the BTAs with gigs, mags, or LTAs so no direct experience with your unique situation. FWIW, for the price of CSBs, I wouldn't mix them. They can recover but sometimes no amount of treatment or removal from the system and into its own system can recover the anemone. Best of luck!