Tyson has always visited you, and he gets along well with his step-brothers (whom you adopted, since only your spouse is in the picture for them).
It's kind of funny, but your step-sons actually have less trouble with you than your son does. Austin and Dallas have grown up with you, they know and understand your rules and limits, and they know what happens when they break them (it involves bare, white bottoms being transformed to red). Tyson has also received the same treatment, when he's with you, but your ex is rather inconsistent with him, and isn't as strict or firm even when trying to be consistent.
Your ex has recently decided to re-marry, which thrilled Tyson into negative numbers. When he threatened to move in with you, your ex called his 'bluff', and then was shocked when the two of you came to an agreement. Tyson has been living with you for about four weeks now.
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That's not the problem - except in that it's earning them sore bottoms.
The problem is that, despite being over a half-year younger, Tyson is already about 5'3" and has some body hair. Austin is still only about 4'11". It's only been a few weeks since you spanked him, and you know he's barely started to develop at all.
Always before, when the boys (mainly Austin and Dallas) got in trouble together, you spanked them together. Even Tyson has been spanked as part of the group, though not in a couple of years.
So, are you changing your methods, or are the boys going to have to adapt to each other starting now?