With it will melt or vanish away what is within their bellies,

﴿يُصۡهَرُ بِهِۦ مَا فِي بُطُونِهِمۡ وَٱلۡجُلُودُ ﴾
[الحج: 20]

With it will melt or vanish away what is within their bellies, as well as (their) skins

﴿يصهر به ما في بطونهم والجلود﴾ [الحج: 20]

Al Bilal Muhammad Et Al
With it will scald what is within their bodies, as well as their skin

Ali Bakhtiari Nejad
What is in their stomachs and their skins are melted with it

Ali Quli Qarai
with which their skins and entrails will fuse

Ali Unal
With which all that is within their bodies, as well as their skins, is melted away

Hamid S Aziz
Whereby that which is in their bellies and their skins shall be scalded

John Medows Rodwell
All that is in their bowels, and their skins, shall be dissolved

Literal
What is in their bellies/insides and the skins is being melted/anointed with it

Mir Anees Original
and for them are whips of iron

Mir Aneesuddin
and for them are whips of iron