# a sea of glass

"a sea that was as smooth as glass" or 2) glass if spoken of as if it were a sea. Alternate translation: "glass that was spread out like a sea" 

# like crystal

"clear as crystal" 

# In the middle of the throne and around the throne

"Immediately around the throne" or "Close to the throne and around it"

# four living creatures

"four living beings" or "four living things"