اندر آئیں

Grammatically, yes, but in Urdu, the plural form is used for a single person to show respect (honorific plural).

No, for animals or very small children, you would use 'Andar aao' or just 'Andar'.

They are almost identical. 'Aaiye' is slightly more formal and traditional, while 'Aaein' is more common in modern speech.

You say 'Andar na آئیں' (Andar na aaein).

Yes, it is perfectly appropriate and professional.

Use 'Tashreef laaein' instead.

Yes, in a physical sense. It can also mean 'within' in a more abstract sense.

Yes, 'Andar aaein' works for both one person (polite) and multiple people.

Constantly! Listen for it whenever a character visits someone's home.

You can say 'Shukriya' (Thank you) as you walk in.

Yes, if someone tells you they are outside your house, you can text 'Andar aaein'.

The root verb is 'Aana' (آنا), meaning 'to come'.

It is a flap 'r', similar to the 'tt' in the American English word 'butter'.

'Aa jao' is a compound verb that adds a sense of completion or friendliness, but it is informal ('Tum' level).