As I state in my thread, my guy quit growing a long time ago. It's been at 6" for many months, perhaps half a year now.
I am pretty sure it is not a large growing catfish. Not Pinirampus pirinampu. I believe it won't reach a foot ever.
I know your dilemma - the unknown can be exciting but one aims to be responsible too. I'd make a backup rehoming plan and get them. Speaking if which, you can count on me taking them in if ever they outgrow your tanks. I'll pay half the shipping if they arrive live and healthy. Just a thought.