Can C/C++ be choice of keeping all your logic (business/domain) for web application?
Why?
I've two resources (cousins) having knowledge on C/C++ and me also good in C/C++, Python, HTML, CSS and JavaScript. 
We like to utilize our free time to work on our some good ideas we developed together. The ideas require knowledge of web application development. And I'm the only one who has it.
Is there a way they developed the core in C/C++ and I do the rest of scripting for front-end development?
Thanks.
I don't think you should use a compiled language (at least not c++) for web programming. I thought about doing this once too but remember that for any change you'll have to compile etc.
Facebook uses php and it's hip hop application changes php into c++. Maybe you should take a look at that.
Of course c++ (or any compiled language) will be faster than an interpreted language, but you also have to take in account the development time of the web site/app.
Hope this helps :)
C/C++ for Core Logic Development of a Web Application?