In my humble opinion the final solution will cost you something in terms of time, financial outlay, privacy, security. The largest barrier you have as stated by you is low upload bandwidth.
You run the high risk of taking down the entire network while trying to upload the video data. Obviously, you would schedule the upload during off hours say from 12:00 AM to X time. But, all of this assumes the file size is defined and known to offer you a general idea of how long It will take to upload said video.
None of that even addresses the fact you need a solid exit plan in case something terribly goes wrong.
Meaning say the video backup hasn’t completed and the remote site is now open. The people onsite have no Internet because the line is saturated you’ll need someway to terminate that running process or have someone do the same.
The first time you have to explain to a client why there’s no internet or why they are tasked to kill a program. You’ll get fire and brimstone for hours assuming you don’t get fired / sued.
Testing & Validation of the above (Exit Plan) is a must and given. I have been involved in multi million dollar sites where so called professionals had no exit plan (DR) Disaster Recovery. To ones that were great on paper and met all ISO / ITIL standards but never consistently tested and validated the same!
The bulk of the DR was the lack of human follow up. Whereas the remainder is a huge reliance on automation not well tested in a Live Environment.
Think AWS failure that took down thousands of companies because a single piece of code told all servers to not fail over. Think Microsoft Azure, O365 because a single Node was stuck bringing down the entire service.
When our team completed the Post Mortem once again human error, failure to test & validate in a live environment, too much reliance on automation & recovery.
People in the NOC Team just too stupid and incompetent to read & follow the break out book, assuming it existed and was current.
So keep that in mind regardless of what I offer below.
There are several options which I’ll just state in very general terms which all have pros & cons. I won’t even bother stating the obvious of privacy & security because it’s a given.
But some of the listed options offer less risk.
Let’s just assume from easy to hard from a local solution to remote solution. You already have 1-2 of the solutions in place in terms of video storage. Edge recording from the camera and stored on the local NVR this is in place which is secure.
This doesn’t address remote viewing or relayed data off site.
Some of the Hikvision NVR’s allow personal cloud storage via Drop Box, One Drive, Google Drive.
This is easy to setup, relatively secure, and all three offer cloud storage pricing at reasonable pricing.
This would allow you to view historic video off site while having two copies from the camera / NVR.
The next solution would require a 24.7.365 computer to run one of any dozen pieces of software to either backup locally or to a offsite storage. Again Hikvision offers similar
tools to accomplish this along with other 3rd party vendors.
Once the data was stored on the target PC. That 3rd party software would upload the video file to whatever destination you choose from cloud to your remote site. All this depends upon how you plan to relay the data out the network.
This also assumes you have set up the network to use Port Forwarding, VPN,
DDNS, P2P, FTP, RTSP, etc.
Let’s ignore the above for now but offer a simple solution just to consider because it can be done. Whether it’s ideal and secure is up to you but it’s just an example of what’s possible and if managed could be a break fix solution.
Again upload bandwidth is key. But this in a round about way removes storage issues and having to pay for the same.
You can create a YouTube account and live stream each camera RTSP stream to this Secure (Private) account using any OBS software. This will allow you to view the live stream for 12 hours. You could bypass this time limit simply by running the live stream when needed vs running it continuously.
All this requires is the OBS software on a local 24.7.365 PC. YouTube account and configuring the IP camera RTSP.
As noted early on if you backed up the video to a local PC. Using almost any FTP client could be used to relay that video data to a offsite storage whether it be cloud vs yours. At the same time use the Live Stream if YouTube / Other Service to view different cameras.
Regardless, the consistent theme is there are ways to do X. But this comes down to what your willing to compromise in terms of real time access, quality of video, to business impact, security & privacy.
It’s going to cost you time & money somewhere but that’s up to you. Some issues just need to be addressed and done regardless - bandwidth.
One thing that Dahua has over Hikvision is most of their current cameras offer native RTMP which allows streaming directly from the camera to services like YouTube. This removes the need for a 24.7.365 PC running and OBS software. This reduces energy cost, potential break point, and dedicated network infrastructure.
As noted before you’ll need to find some kind of balance of historical video vs live viewing which hinges on upload speed. Sometimes just seeing static image clips are fine via FTP / email.
I am curious as to the current need and what these sites are?!?
Meaning say the video backup hasn’t completed and the remote site is now open. The people onsite have no Internet because the line is saturated you’ll need someway to terminate that running process or have someone do the same. 
