Kinda spoiler alert
They all know as it occured since the uke wasn’t a slave
lysbet just chose to turn a blind eye around and acts as if lister is still good and this is how he shows his love to the uke, to be faire she took the uke as her personal servant for him to get away from lister for sometime but huge spoiler alert !!!!
she is trying to get the uke married to lister as he won’t be a slave anymore ( eventhough they aren’t allowed to have kids or even if they did they can’t try to be of a high possition i think )
As for the seme i guess he knows and is planning his revenge while doing the most he could

i'm on ch. 27 and i just can't understand why sylhan doesn't tell anyone what that disgusting scumbag lister is doing to him, i'm so angry i hope lister suffers for the eternity instead of just dying ヽ(`Д´)ノ