Sayf123

Hi Sayf
Regarding the Victron, you don’t get a 5kw unit, that would be 5kva with a power factor of 0.8 making it 4kw. Victron is a good product but the downside is that it’s pricy vs other brands. It’s possible that with the Victron setup that it would deliver more than 4kw on an phase by taking power from the other inverter due to the Victron passthrough function. Sofar solar is a good brand but you would need a high voltage battery. 
If you don’t have any 3 phase equipment then the best would be to convert the DB to single phase depending on your peak power consumption and then have 2 or 3 inverters in parallel on that phase. 
 
I have installed a 3 phase system but it was 3 x 5kw Sunsynk units with 4 x Hubble AM2 batteries. Depending on your needs, I would convert to single phase and do 2 x 8kw Sunsynks in parallel.