Yojimbo-To gain this aeon you must atleast have 216,001 gil or more. 
After you beat Defender X go down the valley that he came from. 
You will see cave proceed inside until you find a dead summoner. 
She will call Yojimbo so summon Bahummut he will make quick work of
Yojimbo.  Then get on the teleport pad and go inside the chamber
of faith then the faith Yojimbo will ask you what you seek. say
"To destroy the most powerful of enemies." he respond
"If you want my strength you must pay the price."  Make
your starting offer as 205,000.  Then make an offer of 216,000. 
After that make an offer of 216,001.  He will accept you offer
and now you have the aeon Yojimbo.

Magus sisters-To get the Magus sisters you must first have all of the
aeons including Yojimbo and Anima.  First go to the Remium Temple
and defeat Belgimes Bahummut she will give you the flower scepter. 
Then capture all of the feinds on munt. Gagazet.  After that
return to the monster arena owner in the calm lands and he will give
you the blossom crown.  Go back to the remium temple and use the blossom
crown and the flower scepter to open the sealed door now you have
these extremely powerful aeons when they get there overdrive they do
500,000 damage.
Enjoy!