||Although I don't like the final answer, I'm willing to stipulate that halachically an adoptee should not sit shiva for an adoptive parent. You're the Rav...not me. (please correct me if I am wrong...that the adoptee SHOULD NOT as opposed to IS NOT REQUIRED TO).
It seems that most adoptees would want to sit shiva anyway. It is how we, as Jews, are taught to mourn. Much has been written about the need to mourn in this fashion: shiva, shloshim, 11 months of availut.
What shoul be the role of the community, the shul, that local orthodox rabbi, etc. if the adoptee decides to sit shiva regardless?
It would seem that the appropriate (supportive/kindness if not halachic) thing to do would be to honor the adoptees choice in mourning. But if they are halachically wrong, then should they be supported?
Is there anything wrong with people paying shiva calls or davening there (assuming the adoptee will be saying kaddish)? Should the shul NOT send a Torah, make announcements, etc.?