Dude you are totally confused and your writing style sucks, lol!
You can have at least 6 lines per account/subaccount - 5 lines in a family share plan and at least 1 individual plan. So no you are wrong, you are not limited to 5 lines per account/subaccount. However, you cannot have more than 10 lines total in your name. So you could have this for instance:
Main Account - 5 FS lines + 1 individual line
Subaccount - 4 FS lines
I have AOLed 3 lines so far and none were told they had to change and in fact they didn't change. You need to tell your buyer to tell the rep that they want to AOL the line exactly as is no changes and they will do it.
They ABSOLUTELY CAN AOL a line as a single line family share plan if that is what they want. They then can add UDP lines to that plan themselves via apple.com.
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Clearly English is not your first language or if it is, you went to the public schools, lol!
You are too dense as to not know you just contradicted yourself. I'm done.