Hmm... trying to think of what the motive might be to assassinating the twins...
Maybe they’re afraid that allowing those with commoner blood to gain power, even indirectly, might set a precedent for others with commoner blood to also gain power?
Perhaps the twins being acknowledged as part of the imperial family could be a huge morale booster for illegitimate children looking to climb up the ranks of nobility. In a previous chapter, it was mentioned that many illegitimate children of nobility existed, but they were hidden away. The twins were not hidden away, which may be used to justify nobles acknowledging their own illegitimate children. This may in turn slowly give more power to commoners, as nobles with commoner blood may be more likely to empathize with them. More power to the commoners mean less power to the nobles, which may be what Count Clone is afraid of. I dunno... just spitballing ideas here... >_>