A treatise on a remote city.

The Rambam rules that the children of the workers in the remote city are also killed, but the Manach makes it difficult. If so, witnesses who testify about the remote city cannot be punished for "when they plotted," since you cannot kill their child (for him or his offspring), and if so, this is evidence that you cannot plot.
My rabbi explained that the plot to kill the children was not a plot against the worker himself, but rather a plot against the children as "the children of a worker in a remote city," and if so, the witnesses plotted to kill a few people and nothing more. (This is not similar to the witnesses testifying against the son of a divorced woman, where the impermissibility of killing children is a consequence of the impermissibility of killing the father).
I am not entirely sure that I would accept the excuse even if it were not for Maimonides in the Laws of Repentance (Chapter 6, Halacha 1), who says that part of the reward and punishment in this world are repaid by a person with his body, his property, and his young children, since young children are like a person's property. In that case, the problem returned to the Dokhta, since they plotted to harm his property, such as his children, and their plot was not carried out.
I wanted to know whether, in the Rabbi's opinion, it is possible to bring evidence from the Rambam in the laws of repentance, that is, does the Rambam, even in the halakhic sections, only write laws that can be determined precisely?