I have 1 farm account and 1 base raider account in the same alliance, how can I attack my farm account..

Your farm need to be in a different alliance (or not in an alliance) for you to attack it. Make your farm leave the alliance and then attack. You can invite it back in afterwards if you want to.

It's generally a good plan for an alliance ot have a second alliance set up as a farm alliance. All the members of the main alliance can place their farm accounts there. You can then declare it as protected by your main alliance.