Have just purchased a new home which has come with three pre-installed security cameras. 

They are in quite hard to access areas due to the size of the home (two story) so am looking at connecting into them. There is a box in the garage where all the cameras come into with a POE switch.

One is a Hikivison which looks like a half decent model, the other two I am unsure of as I cant get a close enough look at them, however, assuming they are the same.

I have had IP cameras before and have used both a Synology and a QNAP nas to manage these, however, at the time i was also using the NAS as storage, to which i wont be now.

Ideally, would like to either connect them to a NAS (either Synology or QNAP) or go the cheap route and hook up an external hdd for recording to my NUC and run them via there.

The Mrs likes having an app on her phone which can give alerts (we have Arlo wireless setups at our current house, which we will either use at the new, or sell if i can get the other ones going and they are decent quality)

Any suggestions for something i can use for the cameras, with recording capability and an APP for IOS?

Thanks!