need to separate them for longer.
you can exchange their bed so they both get used to each others smell
I used to use the same brush to brush their hair
its normal for the bigger cat to me more aggressive as he is trying to show the new cat that he is the boss, as soon as he does that again, you should shout at him and ignore him for at least 5 - 10 mins (no eye contact either) as punishment
when I introduce a new cat to my then 1 year old female cat, she hated the new cat, they used to fight a lot, then suddenly they become friend and start sleeping together.
when you are letting the two cats meet each other, worth doing it in a bigger room which either have plenty of room to hide.