Run the following commands:
/bossbar add b "1st boss health - Correct"
/bossbar add c "2nd boss health - Not correct"
/bossbar set b value 8
/bossbar set c value 8
/bossbar set b max 16
/bossbar set c max 16
/bossbar set b style notched_20
/bossbar set c style notched_20
/bossbar set b players @a
/bossbar set c players @a

It shows: