1- Assuming these hadiths are authentic (the Imam really said those words), then one meaning is that he is speaking about pure human emotions. Ismail was older so Imam Sadeq (a) had more human memories or him, so emotionally he was more attached to him. This is very natural. Sometimes a person can have two sons, and he knows one is much greater than the other, but since he spent more time with the lesser one, he feels a greater emotional connection to him. And at the end of the day the Imam had human emotions too.
2- Here Bada’ means Allah revealed to the people, not the Imam. Imam Sadeq (a) knew very well who the next Imam would be, but the people didn’t. They thought his eldest son Ismail would be, so Imam Sadeq pretended to go with the flow here just to prove to people that Allah chooses the Imams—not him, because if he were to choose, as a father and as a human, he would have chosen Ismail. But the point is that Imams don’t do things out of human nature—they do everything by divine command.