Meaning of characters in 休戚相关, 患难与共
I get this answer from my Trusty translator. (Had to make her a coffee first!)

休：喜悦，吉利 happiness, luck

戚：忧愁悲哀 worry sadness

相关：related, connected

与共： have in common, we share

Edit: Found this link:

http://www.zybang.com/question/ea2bbea8fb9cc6cf808a4790c7900d44.html

From an old song: Life's joys and life's miseries walk hand in hand and keep each other company.

Think that translates it nicely!