Is it permissible for the questioner's daughter to reside with the son of the woman he wishes to marry in the same dwelling, even with a separate room allocated for each of them after they reach puberty, given that neither of them is older than 4 years of age?

It is permissible for a non-pubescent adolescent to look at his mahram relatives at what is above the navel and below the knee. His guardian must obligate him to refrain from looking at non-mahram women, and they must veil themselves from him. As for the discerning child who is not an adolescent, and who is a mahram by lineage, suckling, or marriage, it is permissible for them to be in seclusion and to look at what is above the navel and below the knee.