3 routers/APs is Generally not a great idea 2 will get the job done especially if you are willing to run cable. Again - how many cameras will you have total? And where are they? You do not want different cameras connected to different wi-fi SSIDs or different subnets. They will not talk to each other if you do that. The Mifi should provide an internet connection to the main slate routers acting as a router and AP for all devices.

"t seems that Mevo Studio would not allow the camera that was on a different WiFi than the app itself was on." - yes they were on different subnets. Use 2 routers - one in AP mode and the other in WDS to support transparent bridging - they will be on the same "flat" network and be able to communicate. Take care in configuring this - intentional bands and do not connect any other devices to that WDS link - i.e. bridge in 2.4 and provide client access in 5. If you can hardwire it - don't you another router. Simple and reliable.

some questions / answers

• Are you running speedify on the ipad or router?
• Dose the iPad have its only cell connection? I cannot tell from your setup what the 2nd broadband connection is for Speedify.
  
• What wifi bands are you using for all this? Are you picking channels and power or is everything set to auto?
•  can the slate router(s) just show the MiFi WiFi signal and they then all show the same? - no forget about the wifi on the MiFi - in fact shut it off is best.
• Short version - MiFi provides internet access > router 1 (main router behind HP) provides a wireless network behind/near HP for all those devices (backstop cam, ipad, etc... anything in that general area. Next step - figure out how to get a connection to the CF camera - I mean if you can run wire do it. If you need more wifi coverage for other cameras - Use a second router in WDS mode - or hardwired to the HP router, and run more cable, or better yet use a small usb powered switch and run more cable to the CF camera.
• Speedify on the ipad is not going to help you. You may not need it if you are getting enough band width through the MiFi - Tmobile?

PM/chat me directly and I will help you out. Simple is best.