**** Major Spoilers for both Umbrella academy Season 1 and Stranger things season 1 and 2... continue at own Risk****
——You have been warned!!!——-
I’m just saying if they were born on the same day (October 31st, 1989) then 11 wouldn’t be a teenager in the early-mid 80s. Because she wouldn’t have been born yet. If your suggesting that 11 and 8 were time travelled back in time. That... would also not make since because of 11’s mother. 11’s mother and aunt would have had to been time traveled back as well. Then there’s also the fact that 11’s mother was pregnant with a normal gestation period. Unlike The Umbrella academy children who’s parents were not pregnant when the day first began. Finally Hopper can’t leave Indiana to work on patches case because hopper is a middle aged cop (probably around 40) in the 1980s he would be somewhere around 75-80 in 2019 where patch is a detective. Something tells me with his lifestyle he doesn’t live that long and even if he does that’s a ridiculously old age for him to still be working and much less move from his small town to the City. I can not however completely rule out Dr. Brenner knowing Reginald as Reginald is an Alien who moved to the City in I think 1928 (or at least that’s the date on his card when he goes threw an Ellis island looking immigration center. Both men are interested in Genetics and if they do exist in the same universe it is likely that at some point they have met... be it at an awards ceremony for research or government facility or whatever.
——I Warned you there were spoilers for both series——