Can I add my android phone to my iPhone as a second one

From the article linked above:

"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."

A cellular plan involves a telephone number dedicated to a specific device. You may not use your Android's cellular telephone number to access calls on an iPhone in this manner. Perhaps you may forward calls if your carrier offers that option.

You can’t. Any phone number can be associated with only one phone, regardless of model.