The maximum load is specified by the manufacturer as 100kg.

In principle, three people can certainly stand on it. There is enough space. You see many people on the lake who are on a SUP with two or three people.
The question is rather for what you need it? On the river, I don't recommend using it with three people. The excess weight makes it harder to steer.
On the lake it can certainly be used to a certain extent, but here too it is more difficult to steer. And getting into the wind or against the current is no longer easy. SUPs are actually individual devices.
In addition, the manufacturer's specifications should not be disregarded.
Why not just buy three at once?

Hi,
I can agree with Heinzi for the most part. It is certainly still possible with two people, I managed it with my colleague (both around 70-80 kg).
If you want good manoeuvrability, it is not suitable for two/three, but if you just want to enjoy the sun on the lake, then the SUP should be enough.