[Souten no Seigyoku]

No it makes sense that they summon their former masters' pets.
Kish is saying they are the New Sanin and have surpassed their masters.

The frog boss never died.
Katsuyu is the name of the slug. Its Tsunade's slug. Hasn't died either
Sasuke's snake- another snake. Manda died a long time ago. Kabuto's Manda is a clone.

While Naruto was in Mount Myoboku, we all saw how there are many frogs. He as summoned others as well. He summoned 3 big ones at the start of the Pain fight. It's the same for Sasuke.