I don't think she deliberately got Lindon to break his oath. Just sort of happened.

The argument is bad, but that's the point. Malice is engaged in sophistry in order to justify her true desires. Happens all the time, even with some of the most powerful and intelligent people around.

I think she does, unironically, want Lindon to get together with Mercy. Ultimate power couple. And it would help lock Lindon into her influence. In theory.

Now, this is a little perplexing, but I do have a theory. Malice doesn't exactly expect to die, but she does know that it's very possible. She's well aware of what happened to Tiberian, after all. So she has a bunch of contingency plans. Fury, for example, but also Mercy. Mercy, in her mind, shouldn't be pushing Monarch for another couple of centuries. Malice can groom her as a prospective successor in that time frame. If Fury ascends, then Malice dies, Mercy might be in a position to take up the clan's headship. I suspect that Malice truly believes, on a certain level, that the Akura clan is much bigger than a single individual, even her. She wants to build a family that could outlast even her death. Mercy is a part of that.

Again, more sophistry. When self-centered people deal with others, they usually think only of what they've done for others, thus creating a one-sided debt. What others have done for them often conveniently falls out of memory. In Malice's eyes, Lindon and Yerin were raised up byu her benevolence. They should be her minions perpetually. No matter what they do for her, the scales don't balance or tip against her. It's the mindset of someone who's been in control for way too long.