Are Sunsynk and Deye inverters manufacture by the same company and what are the difference

Deye manufactures Sunsynk, also makes Fusion, Inge and SolArk (in the U.S.). Sunsynk has a slighly better user interface, and by the looks of it better support. It will also soon have its own proprietary monitoring and control system. 

Yes, the Sunsynk has a slightly better user interface but I have found the Deye to be absolutely fine, even maybe a bit more intuitive.

But using something like Solar Assistant on any of these makes, makes it all pretty universal when it comes to monitoring and remote system management.

MdF

Same inverter different firmware. I personaly prefer Sunsynk after installing a few of both.