Are the following sentence correct?
How could somebody go to school with another person constantly but barely know that person?
Don’t you think that anybody who has the true intention to practice would have made sure that they can get into the theater?

Question

Answer

First sentence is correct grammatically.  You might want to put "constantly" before "go".

The second sentence is not correct because "they" should be "he" or "she".  It's awkward to write it this way but that's the problem with English.  You could write:

Don't you think that anybody who intends to practice would ensure access to the theater?