I suggest that you look at other discussions, there are some really great answers there with similar/same questions.
To summarize since it is official that it is Minerva. We don't KNOW she was born in 1935, all we know is that she has worked there for 39 years as of 1996 and she was 20 when she started working there. We don't know that she worked there for those 39 years in a row. People did the math and arrived back to 1935, but nowhere are we actually told 1935, just October 4th. Dumbledore taught D.A.D.A. in 1927, so we can assume she taught Transfiguration during that time. We know Dumbledore taught Transfiguration though at some point, so it is possible Minerva left Hogwarts doing work for Dumbledore and during this time he took over teaching Transfiguration, then she returned years later and took up the mantle again when he became Headmaster. We don't know the story, but it is clear everyone was wrong when they assumed her birth year.
I think that the girl on the boat was Albus’s sister who’s baby got swapped by Lita. Then the baby who drowned was Lita’s brother and the girl who went after him was Ablus Dumbledores sister, because earlier in the movie Arbus says to Lita that his sister died. So the kid Lita switched is Credince. (Sorry if speller wrong where I am it’s 11:40 PM and I’m tired)
I completely agree with everything you’re saying
That's definitely not Albus's sister. We have known for a long time that Albus had a sister and that she died at age 14. Her name was Ariana and she was killed in a fight between Albus, Aberforth, and Grindelwald. We see her ghost in Deathly Hallows Part 1(?) in Aberforth's house. So the lady on the ship is not her. She's identified as Aurelius's "aunt", but I think it's referencing Albus's aunt Honoria and it's actually his mother.