is ot possible to have 2apple iid's

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

What happens when you use the same Apple ID & Password that you use to sign in here?

See the following Apple articles

Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

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See -> About eSIM on iPhone -> About eSIM on iPhone – Apple Support (UK)

An eSIM is an industry-standard digital SIM that allows you to activate a cellular plan from your carrier without having to use a physical SIM. You can install eight or more eSIMs on an iPhone and use two phone numbers at the same time. 

About eSIM on iPhone - Apple Support