ANSWER:

This is not part of Islam at all. 

You can invite people to your home for lunch or dinner but doing this thinking that this is something required after Hajj or thinking it to be from the Sunnah is totally wrong.

My mother’s brother has performed Hajj this year and now he messaged me to invite him to my house for a small party (Lunch), because he has performed hajj . Even my aunt is insisting me and my mother to invite him for lunch and offer him a floral garland to be worn. Please advise is this permissible? Because many people are following this tradition.