Battlelines and battalions are 2 different things.
For starters if you want to have the Khorn Allegiance, you need all of your units to have the keywords: CHAOS, KHORNE.
If you want to use units that are not KHORNE, but have the CHAOS keyword you need to check the rules for using Allies.
When it comes to Battlelines, in the General's Handbook or your Battletome, at the page where it says the points of each unit, it also writes the type of each unit.
There you will find what unit is battleline.
The rule for a game of 2000 points, is that you need to have 3 battleline units.
So check if the units you have selected are battleline or not.
For battleline you can use any unit that has that type. The allegiance is determined by the keywoards of all of your units.
So at first it seems that those above rules and independent to each other.
The only exception is that some units "gain" the battleline type, if the whole army meets certain criteria.
For example I believe that some units gain the battleline type if your whole army has certain allegiance.
So in general, if you have allegiance of KHORNE you can use any unit that says it is battleline regardless if it has the keyword KHORNE or not.
But if you use too many non-KHORNE units you may loose the allegiance.