A) personally, i don't think Krillin should be in the game bcuz he in reality is just a chew toy for enemies to kick around and waste episode time. When is the last time after frieza fight (even then he didn't do much) that he did something good? He is too weak to even remotely stand a chance against normal Goku, nm SSJ and SSJ2 Goku. Goten could kick the crap out of him.
B) I don't think Goten would be a good addition unless they added chibi trunks too. Goten is a good fighter, but still didn't good much in the show other than Gotenks. I think that Goten should only be added if Trunks is. And for gotens transformations, he could be Normal>SSJ>gotenks>SSJ gotenks>Ssj3 gotenks
That would work, and then let those transformations go on ith trunks too