We have to cut ( ) both of your legs?

out

cut out
To remove by or as if by cutting.
切去，删去：用或似乎用切割来去除

off
cut off: 切断

cut sth away (from sth)
（自某物上）切除, 剪去, 破掉某物
They cut away all the dead branches from the tree. 他们把树上的枯枝通通砍掉了.
所以用away。