Regarding Custom Loader and iFrame

Hello,

i have Stape account and one sGTM container.
At the moment I would like to implement iFrame to my website and create a Child Container in GTM.

Should I create a new sGTM Container in my Stape Account and use custom loader for my Child Container?

Or I can use current sGTM Container and generate a new custom loader using child GTM ID ?

Greetings!