Creating responsive web app for different platforms/device

past two days i was searching for a solution for my problem. I searched a lot inside the stack over flow( if I missed please correct me ). It didn't meet my needs.

First of all please let me discuss my problem : I am completely from windows application (C#) background. Currently I am working on a solution (Windows Application) with 54 projects and I am handling a big database(SQL) with more than 600 tables.In this solution we are using EntityFramework and its working very fastly and perfectly.

So my problem is I need to make some reports online (WebPage/WebApplication). For example Purchase reports or Sales reports daily, monthly and yearly basis and these reports should able to run in different Platform/Devices (eg: IOS,Android,Windows tablets or Phones). Especially because of reports I need to apply some filteration to reports, So I need to place controls inside it (eg: from date - To date ..etc)

Most of the time our client will use this on computers, but if they are on site they will use the tablet or Phones. I found one question as same as mine, its here-

Creating an Application for different platforms/device

This question asked on 2012, as my knowledge i know that technologies grows very fast. So I think there is new/better solution for my problem. And in that question they didn't discuss anything about handling databases inside the Application. I am also looking for high performance interface, because the database is huge. Making query against the database will slow down the App performance.

One thing I would like to remind, I cannot change my database. If your kind mentality is going to help me in this situation, please suggest something that able execute/support the SQL database also.

Thank you !