They should not sell. You just can't do that within a game or two of a playoff spot.
But they also should not buy with real prospects. A combination of being able to add $15 million in salary and 3rd tier prospects should be all they can risk. If they make the playoffs it is because their young starters actually pitch well or some players like Harper and Hoskins start hitting. They do have the talent to win 86 games. They just don't have the talent to win 92 and the division.
I would also think about making Haseley the starting CF and Kingery the starting 3B (assuming Segura is not hurt). Franco is just not helping the team since his defense is mediocre even if he is hitting.
Nothing to really do about the bullpen other than getting some veterans in on the cheap.