They have a couple memories of being together in the orphanage when they were very young, but they both got adopted separately and grew up far apart. It does not feel incestuous at all. More like childhood friends meeting after a long time.
Thank you for your answer. I will continue reading for now and update this topic if anything arises. I have been concerned over plots like this with the tag "Romance" as often times there are similar stories that lean into the incestuous side.
Update.
Around chapter 20, it seems noticeably implied that Amelia and Thomas has a non-platonic crush on each other, or at the very least supporting characters joke they are flirting. Dropping this manga due to the implied romantic tones up to this point, and potential confessions and so on in future chapters. It is solely due to the fact that I do not hold high interest in stories with a big focus on romance.
Hello. For my own comfort, does Amelia and Thomas become a couple, or is implied to be romantically interested? I am not interested in storylines where adoptive/orphanage siblings become romantically involved.