Hey Haewon! No problem ^^
Your process looks good! "These" is grammatically incorrect since it is in the wrong pronoun form. "They" = subject case pronoun, and it is the correct form.
Extra Tip:
On the SAT "these" would be considered unclear if it is used by itself.
ex.
These were the best I have taken. (Unclear pronoun)
However...
If you say "these people" or "these schools" or "these books" the word "these" now functions as an adjective, and the phrase "these school" is now considered clear. =)
ex.
I traveled to Hawaii in 2011, Japan in 2014, and Korea in 2018. These trips were the best I have taken.
The phrase "these trips" refers to the specific trips mentioned in the previous sentence.
Hope that's clear!
You got this! =)