"Vos" means "You" (in the sens of "ye", as you've correctly translated at the end)
"Rosarum" is the genitive plural of "rosa" meaning "rose". You can translate "flores rosarum" as "rose flowers/ rosy flowers/ roses"
"In effusione sanguinis vestri" means "in the shedding of your blood/ in your bloodshed"
As a whole translation, I would propose:
"You rose flowers
Which are blessed
In the shedding
Of your blood"
I can't judge your translation skills from 4 lines, so I give you 4 stars because I appreciate the effort.