As per Rashi's commentary on Bereshit 35:22, Reuven did not actually lay with Bilhah, rather, he simply moved Ya'akov's couch. On this account, Reuven sinned and was deprived of firstborn status:
וישכב AND HE LAY — Because he had disturbed his couch Scripture accounts it to him as though he had actually sinned in this manner. But why did he disturb his couch? When Rachel died Jacob removed to Bilhah’s tent and Reuben came and protested against the slight thus inflicted on his mother (Leah). He said: “If my mother’s sister was her rival, is that any reason why the handmaid of my mother’s sister should become a rival to her!” On this account he disturbed the couch (Shabbat 55b). (https://www.sefaria.org/Genesis.35.22?lang=bi&with=Rashi&lang2=en)
Now, I am the firstborn son in my family, and I am renovating my father's house while he is away. When it comes time to redo the flooring in my father's bedroom, will I be sinning if I move the bed for this purpose? Further complicating matters, we are kohenim (and therefore B'nai Leah), my mother is a Bat Yirsael, and my father is remarried.