I would second the idea of a little email or letter, imagining that it could be forwarded to anyone so the information might want to focus on more how you would prefer the to interact wkth your child rsther than them drawing conclusions based on some misinformation they have conjured from their own imagination. In our intro letter to family we covered:
The names of the kids and their ages
That we would be their only parents, and that legally and practically they will have the same rights and status as BC.
How we expected people to refer to them- I.e. don't always use the word adopted, they are your cousin, grandson etc
Time we would be bringing them home and when we would visit or allow visits
Something along the lines of: we may be parenting them slightly differently to the way many children are, and they may respond differently. This is in accordance with the training we have received and professionals we are working with, but if you have any questions or concerns please direct them to us and not the children. Everything we do is intentional.
We also included a few podcast recommendations and links to articles that people said were helpful, but were not specific to our children per se.
Obviously this was all in a chatty lovely tone super friendly, but it helped to set the boundaries without giving information out.
We found that people's response to the email gave a good indication of how supportive they would be, so it was a good litmus test. Those who got huffy have been less supportive and more undermining. Those who were chill with the email have generally been more chill with us.