Family plan and migrating to telus

"Is the family plan all numbers under ONE single name and one large bill vs 2 smaller bills in our case?"

Yes, one bill, one account owner.

"its been years since ive migrated a telephone number from one service provider to another and i remember that things had to be exact at both ends will there be any issues moving the second line from one name to a new name at telus if the family plan is only under one account?"

The best process is to set up and port the primary account  phone number from Koodo. Once that is complete, you then set up the second service on the account, and port that number. If at some future date you wish to separate the two numbers to two different accounts, the primary account holder will need to authorize the porting of the number to the new account holder. 
BTW, you will need the credentials of both Koodo accounts to complete the port.