You wont like the answer but if you want to max all three summons then quit your group and you and your members should join the biggest group with most members. Then you pool your chakra to culitivate summons. There is no way for small or medium sized groups to cultivate the summons. You probably need group activity level above 500 or so. At 400 based on what I have seen you wont have enough members to cultivate. Oasis should probably make cultivation dependent on the number of members rather then having it the same for big and small groups but that is the situation