Filing the I-130 with the CP option is not a strong indicator of immigrant intent, and the fact that CP was chosen can be used to help convince the IO that they plan to leave the US for the consular interview instead of staying and attempting to immigrate.
If you haven't filed it yet, wait until after they arrive in the US and then file it, so they won't have to answer questions about it at the POE. With the CP option, there is no need to wait 90 days or until they have left the US; you can file the I-130 same day they arrive and it won't increase the chances of denial provided that they actually leave the US before their B2 stay expires.