Is a couch that has been wiped twice with a cloth considered pure after it was touched by urine that was not washed away? And does the house become impure by the visit of relatives who do not care about keeping their homes free of urine, and what should be done?

The rule for removing impurity is to wash it with pure water when the contamination is confirmed. As for doubt, sprinkling is sufficient. The sofa your brother sat on, with trousers from which impurity was removed with water and soap, does not become impure by that. If the impurity itself is removed by something other than pure, unmixed water, the place it touched does not become impure. As for doubt about impurity affecting the sofa or other parts of the house from children's urine, sprinkling with pure water is sufficient.