Going to peoples houses for khatam

Q: People call me to there house for khatam. They say sit in the middle and they tell me we have done e.g. 10 katams of Qur'an, many thousands ayaat-e-karima and I do dua for the diseased then we eat. Is it permissible for me to eat? They also give money at the end. What is the Shari'ee hukm with reference?

Congregational Dua

Q: One person who has ta'lluq with the salafees told me that making dua with jamaat after salaah is not established. Therefore we shouldn't make it in group. Rather each one should make his dua separately.