In a family of four, one member has an exalted planet and another a debilitated one. Whose chart decides the paintings and colours?
The house is planned from the chart of the head of the household. A member who has a separate room, such as a son sleeping in his own room, can have that room done according to his own chart.
Related questions
A couple sleeps in the SW; one has an exalted Rahu and the other a debilitated Rahu. Can they sleep there?
Yes. After marriage, as in the hathleva ritual, the planets of one partner overlap the other, and the exalted planet's influence prevails.
If a house has four members, whose kundli should be used for its vastu?
Primarily the grih swami's, the person whose money is going into the house, because the house affects the owner and his next three generations; do not go by the name the property is registered in, such as a daughter. The facing and main door are chosen from the grih swami's chart, for example North if his Mercury is exalted or his North-side planets are strong. Where a child sleeps or studies is decided from the child's own chart: if the child's Mercury is weak, seat him in the South instead of the North, following the 180-degree rule for a weak planet.
If one family member has a planet exalted and another has it debilitated, should that planet's items be kept in the interior?
Decide room by room. In your own bedroom use the materials of your exalted planet and not of your debilitated one; your daughter's bedroom is designed from her kundli. The house facing and common areas such as the drawing room and kitchen are decided from the grih swami's kundli. Many people make the master bedroom in the South-West by default, which is wrong when Rahu is debilitated: such people suffered there and got very good results after moving to another direction.
In the case where all four family members had a weak Sun, why would four separate kundlis show the same pattern?
Members of one family almost always have nearly the same planetary placements; there is a symmetry among their charts, and that is why they are born into the same family. In that case the Sun was badly placed in all four charts, so the East-facing house harmed the whole family.
The 5th lord is Mars but the child studies in the West. Is that wrong?
See in which direction the 5th lord sits. If it sits in the West, that is excellent; if in the East, choose the East. The East and North are best for study anyway, and if the lord sits in the South, studying in the South also works.
Why is sleeping recommended in the South-West or the South?
Sleep is an activity of Saturn, and Saturn is a friend of Rahu-Ketu, who rule the South-West. The South is the seat of Yama, before whom no one prevails. Sun and Saturn are enemies, so sleeping in the East brings husband-wife quarrels; only a king-like person such as a politician or minister can sleep there. Applying this friend-enemy logic of the planets to every activity lets you derive remedies yourself.