How secure is this in terms of privacy ?
One can only guess: If the data are not encrypted for transport they can be easily sniffed. If the data are encrypted for transport but not at rest a hack at the cloud storage might make them available for others. If they are encrypted for rest but the provider of the cloud storage has the key they can access these. If they are encrypted on the origin device and a key is only shared with the viewing device it might be safe.
Note that in all these examples encryption means proper encryption and not some self-made algorithm or messed up implementation of well-known algorithm or weak algorithm which is often done by less experienced developers and/or because of hardware constraints on the device. The same is true for key sharing.
Apart from these a passive listener might notice when and how many data are transferred and thus make assumptions about the activity (some CCTV send only when they notice activity). And depending on the system it might be possible to block transmission of data without notice to the viewer or even replace it with different data.
How can we stream this video into our own cloud environment and view from the mobile? Can we set up our own cloud back up as well ?
That's a product specific question you have to ask the vendor.