1- Saying “Yarhamuk Allah to a person who sneezes, if he says “Al hamdu Lillah (praise be to Allah),” is a communal obligation 2- If a person sneezes more than three times, you should not say “Yarhamuk Allah” to him; rather you should pray for his well-being. For more, see the detailed answer.

Visiting the sick is a confirmed Sunnah. The reward attained by the one who visits the sick is likened to the harvest reaped by one who gathers fruit.