I think they are running at normal temperature and 950 hours, I have seen several YouTube videos of the same boat as ours Atares 10.80 producing vapour, the owner before the current vendor says they made vapour in the two years he owned, no sign of diesel injectors, exhaust gases not blackerr no.
Are the engines running at the correct temperature? check with an infra red thermometer as the gauges aren't very precise.
If the engine temps are OK remove the exhaust elbows and have a look inside. It could be the water injection path is bunged up so cooling/exhaust water is getting boiled and making lots of steam.
That exhaust looks a bit grey too, probably just the picture. How many hours and have the fuel injectors been serviced at all?