There is a incest patch for it. Lewd Patcher - Uncensored patches for Patreon & Steam adult games. It is like this because he wants to stay on Patreon which doesn't allow incest, instead of switching to Subscribestar which does
Thank you very much about your comment. After reading the explanations provided with the patcher I understand the game a lot better. For me up to now a tenant was someone to lease a room or an apartement from a landlord oder a landlady. Not that it spoils the game but the original version adds some spice.