He was fired from his past job for expenses irregularities. My partner can't see his brother's faults, but I know I should put a stop to this plan. Can I do so without ruining our own business relationship?
A: Even the relatively sparse information contained in your question gives me the strongest possible sense of what this brother is like. I bet he's one of those nerveless operators; never too concerned about the borderline between being smart and being bent; who likes a bit of gold about his person; and who's managed to get away with murder since he was nine on the strength of a telling way with words and a tyrannically engaging personality.
Nobody, of either sex, wants to fall foul of this flawed but fascinating creature - and so their normal critical faculties are put on hold.
It's not that your partner can't see his brother's faults: he's been only too aware of them for as long as they've known each other. It's just that he, like the rest of the world, finds the charm, the confidence and the ruthless exploitation of personality just too overwhelming to rebel against. He is, in a word, intimidated.
So I suggest you be absolutely adamant about this: under no circumstances must you countenance this brother becoming a partner in your firm. Your existing partner will protest, throw a few wobblies, threaten to withdraw his equity - and will lay all the blame on you when he tells his brother.
But at heart he will know it's exactly right and will feel a sense of relief that you've taken it off his shoulders. Do not, however, expect him to express gratitude; and under no circumstance fish for it. But it means that your relationship can survive and even be strengthened.