Selling Items Related To Non-Mulsim Celebrations/Festivals

Every item which is Halaal in itself will be permissible to sell. Items such as alcohol, pork and any animal which was slaughtered un-Islamically are Haraam and therefore impermissible to sell. Items which contain any ingredient made from these will also be impermissible. For example any food items which has alcohol in them, brushes which are made from pig hair, gelatine which is made from any part of a Haraam animal; all these will also be impermissible.

It is permissible to sell gifts and promotional items for occasions, provided that they are not Haraam objects (such as musical instruments or dolls, statues etc. of animate objects) and not connected with any religious festivities of non-muslim communities. 

Hence, you should not promote and sell items that have religious or/and customary connotations with the Hindu’s Diwali or with Christian festivals such as Christmas and Valentine.