I know I can access the open, close, high and low with Open / Close / High / Low.
What about the other prices in this same bar ?
No such things. M1 is the smallest timeframe stored.
Get tick prices - this is your friend - https://docs.mql4.com/constants/structures/mqltick - convert the time to second and find if you already have other ticks with same time (like in same minute/ second or hour depending on what you wish to look for )