I wish to have a good relations with sister in law and will try to make dawah but how can I reject their invitation & still be respected? I don’t want to break their hearts by declining but I’m not willing to bend my beliefs for their indifference.
Your approach is correct and commendable. It is important to maintain family
ties and that will be conducive to your intention of making dawah to them.
We suggest you request them to prepare a vegetable dish or a seafood dish as
you are abstaining from meat products due to medical reasons.
And Allah Ta’ala knows best
Mufti E. Desai