1) Having a wifi router doesn't mean you are connected to the internet. You need to connect the router to the internet. Disconnect your router from the internet.
2) Turn off cellular data in your ipad.
3) Set up your ipad to use internet sharing on your pc. Install some firewall on your pc to monitor and filter the internet traffic to your hearts content.
4) Buy a router that you can do the filtering on the router.
Use an app like
"iMazing is the all purpose iOS management software: expand your control over your mobile data beyond what is normally possible, without jailbreaking your device. With iMazing, you can easily browse and manage your backups, extract and print your text messages, or drag and drop songs to your iPhone. To put it simply, iMazing allows you to go way beyond what iTunes offers"
https://imazing.com/
Files Connect -- "Cloud Storage services like Dropbox, MobileMe iDisk, Google Docs/Picasa, Facebook photos, FTP, SFTP, WebDAV ... AFS (Apple File Shares) SMB (Windows shares) protocols"
https://itunes.apple.com/us/app/files-connect/id404324302?mt=8
Windows File server
http://itunes.apple.com/us/app/filebrowser-access-files-on/id364738545?mt=8
Simple Transfer - Wireless Photo & Video Backup, Sync & Share by Rambax, LLC
https://itunes.apple.com/us/app/simple-transfer-wireless-photo/id420821506?mt=8
"Dukto is a simple application that allows you to share files between devices connected to the same (wireless) LAN network."
http://www.tidal.it/?page_id=309&lang=en
http://www.msec.it/blog/?page_id=11
"Transfer files the easy way, just drag & drop the file and we will handle the rest. Like Apple AirDrop, but works and on all major platforms and computers that don't support AirDrop. Apps are available for iOS, OS X, Windows, and Android."
https://itunes.apple.com/us/app/instashare-air-drop-transfer/id576220851?mt=8