Admission in Bachelor's Program

I wanted to know that out of the above three universities which one should I consider for taking admission ?

I think you should leave the decision to your cousin, not decide for him.

Furthermore my cousin is a Muslim and he is 19 years old. So how is life for students at Germany who are studying at bachelor's level?

Life is generally good for students, provided they have enough money - which your cousin should bring along.

While side jobs are allowed, this is mainly for internships and industrial attachments as part of the classes. Since studies are designed to be full-time, it is not possible to earn your living expenses without negatively affecting the course outcome.

Muslims face few restrictions, but if he dislikes people around him eating pork or drinking alcohol, he should not come to Germany - this is an integral part of our culture!

Also, South Asian food and spices are considered exotic delicacies which do not come cheap here. If on a tight budget, he will have to adapt his tastes and lifestyle to what is common here.

Furthermore, please confirm if high school is considered after 12 years of education or 13 years of education in Germany ? Lastly please confirm if undergraduate programs are of three years or four years in Germany ?

This depends on the school and state - some require 12 and some 13 years until "Abitur" (high school graduation). And some universities or courses take 3, some 4 years to a Bachelor degree - plus, there is always the possibility that he needs longer if he isn't studying hard!        -

Germany requires the equivalence of the German Abitur which is a 13 year schooling on the highest academic level. Coming from elsewhere it is usually easiest if one completes a couple of years at university in their home country and then transfers. The major problem with a foreigner doing a bachelor in Germany is that the vast majority are taught in German and one needs a C1 level.

Masters are often offer taught in English. But even at public universities not all bachelors and most masters are NOT tuition free for non-EU citizens. And one needs over 11,000 Euros/year for living expenses, required to get the study visa. Germany has freedom of religion, so that is not even an issue – unless one thinks they can show up and impose their beliefs on others. One can practice their religion but not deny the local beliefs which are mostly Christian. In that case they should choice an Islamic country instead.