True .. its the responsibility of the neighbour. But in this case .. I'm guessing the bills the Mathurs handed over to Shukla were of the decoration lighting and other expenses they incurred during the wedding. Coz when Brij tells Kul that the Majumdars were their guests .. Kul does retort back saying that they were responsible for the accomodation and chai-paani .. but they (Shuklas or Majumdars) need to pay for the rest.
In our community .. the expenses are usually shared equally amongst the bride's & groom's side.