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The chemical elements are there in a same group of periodic table for a reason. The reason is they are similar in many respects.
Every language needs a vocabulary, grammar, construction (which I think is also a part of grammar?), and script, that's all.
What is common between the languages of a same family? What are the similarities between Urdu, Hindi, and English? Are there any?
Urdu and Hindi have a common ancestor Khariboli and have a lot of common features. Urdu is written is Nastaleeq script while Hindi in Devanagari. Hindi borrows many words from Sanskrit while Urdu from Arabic and Persian.
I don't think there ever was any kind of proto-language. Rather, there was a dialect continuum between the people who were culturally, economically, and regionally etc. related. The tree diagram which is used to represent the evolution of languages from the parent language is highly misleading.
Read the first few paragraphs on the linked webpage:
http://paleoglot.blogspot.com/2007/10/language-waves-and-satem-innovation-in.html
Where do the languages of the tribes who live in jungles come from? Do they fit in any language family?