Theseus having a vampire!S/O only to be completely clueless and Newt assuming he already knows
Newt first starts to notice something strange about his new in law almost seconds after being introduced.
Firstly they’d been dressed in all black, which is fine newt just didn’t realised his brother had a thing for goth girls but given his previous relationship he supposed it made sense
Then it was how coincidentally newt only ever socialised with her at night, and on the rare occasion it was light out they were draped in thick fabrics and armed with a parasol
Newt also started to notice strange marks on his brothers neck, at first he believed it was a rash of some kind, maybe even a change encounter with a bellywig. But last he checked insects didn’t have molars like the ones indented in his protege skin
In conclusion Theseus was definitely maybe possibly dating a very obvious (and lovely) vampire. Which Newt didn’t mind one bit and fully assumed his brother both knew and didn’t mind
Actually his brother seemed quite enthusiastic about this new relationship, his hugs had grown uncomfortably more frequent for Newt, which had always been an indication of his brothers general well-being
His brother’s partner was also well mannered, they adored his niffler even when one of them tried to snatch a pendant Theseus had gifted them. Although with one small hiss the creature seemed to back off their persistent pursuits, at least for the time being.
Plus this social circumstance allowed for Newt to brush up on previously unanswered questions regarding their vampirism, all of which Theseus assumes its just Newt being newt
“Do you have a strong distaste for garlic?”
“Do you drink through your teeth or your throat?”
“What would you say your favourite flavour is A or O?” -Theseus thinks he means apple or oranges
“Do and can you go into a church?”
“Can you sleep in a bed?”