In the Shariah, the rules of eating/drinking have been described in detail. Among them is that while eating, we should be mindful of others also. In food, the quantity of every person is obviously not the same, so if people eat together and collectively pay the bill, then even though they have not eaten exactly equal amounts, there is no problem in this. The Jurists have clarified this:
Translation: If the travelers share their meals, or if everyone contributes 2 Dirham and they get food and share it, then this is permissible even though there is a discrepancy in the quantity of food they have eaten individually.
And Allah The Most Merciful and The Most Beneficent knows best.
Mufti Syed Ziauddin Naqshbandi Qadri
[Professor, Islamic Law, Jamia Nizamia,
Founder-Director Abul Hasanaat Islamic Research Center]