I had a look at Chapter 28, kev. As far as I see, Mr Pickwick is regarded as a close friend and benefactor of the bride's family, and besides, one of the witnesses of the wedding. He brings not only himself and his friends to the wedding, but also a lot of choice food. The father of the bride seems not to be a poor man, but the wedding profits largely from Mr Pickwicks contributions in food and in good humor. Probably the relationships were less formal as maybe in other book. And it was Christmas Time. Dickens was writing one of his typical Christmas stories which celebrated the good will and the joy among all the people,where the rich helped the poor, the young the old, the healthy the sick one. He wasn´t so particular about family ties or time of acquaintance it seems, he was celebrating the universal ties of friendship. It becomes easy to understand if you remember, that Dickens himself had to provide for a lot of hungry family members as soon as he became a successful writer.