Are those Bertoia from Knoll  

They are real.
They are real.

any hints to know that they...
any hints to know that they are real
thx

I just know them. That's...
I just know them. That's all. The shape, etc.

I'll help out some.
It's...
I'll help out some.
It's likely a knock off. The welds looks subpar, unless it was poorly repaired. The other questionable issue is how the seat is connected to the frame. Best way for me to describe it would be a bar or track the screws thread through to affix seat to frame. On your chair, it appears the seat is directly welded to the frame. On your chair, there's a "nob" the screw goes through to connect the frame, this is not right.
Th frame looks correct. The welds of the frame overlap. See the front of the chair, the top upper left and right of the frame corners show overlaping welded bars. Most knock offs have a smooth transition.

I'd bet money
... that they are fake.
Sorry to contradict you Whitespike, but they look very wrong to me. I've not scrutinized any knock offs, but I've handled plenty of real diamond chairs. WoofWoof is right, the connection between the seat and base is all wrong. Also from the photos it looks like there is a weld glob where each wire crosses another. That should not be. The Knoll chairs are electronically welded so the wires are attached but there is no additional material added. If it was in one or two places, you could say that the wires became disconnected (not all that uncommon) and were repaired, but it looks like each connection has been welded in this manner.
Additionally, if you look at the detail shots, the wires are not smooth, but wavy and crooked. Again, this should not be the case unless they have been damaged.
Too much looks off for me to think they are anything but fakes.

I agree
Either knock-off or a really bad repair job, or both. The welds look horrible.
Either way, not worth pursuing, in my opinion.

Since these were knocked off
early on, I wonder why on earth Knoll never bothered to put some kind of Knoll trademark on their Bertoia chairs!!??
If they had bothered to mark their products, we wouldn't have to have this conversation.

Maybe not fake.
Didn't the mounting method change partway through the long production history of these chairs? The modern chairs have a flat bar (or maybe it's U-shaped; I'm not at home to check) welded to the seat, but maybe the older ones didn't.
Also, the closeup photos are of the edge and the mounting area -- which are the two places where welds typically break and are repaired, so I'm not at all surprised to see wavyness and less-than-perfect welds in those areas.
I'm inclined to go with Whitespike here, and vote for real... Although I'd change my vote if I were told that ALL the welds look like the ones in the closeup, or that I was wrong about the mounting-method change.

To answer both questions
Barry, the Bertoia pieces were not knocked off early on (like the Eames lounge or Noguchi coffee table) it's a more recent phenomenon. Why? because it was hard to do (until recently) and there was not the demand. The diamond chair was reasonably popular, but not a blockbuster seller or an instant icon.
Knoll does now, and always has put labels on the pads and cushions. Why they don't put their name on the fame now? Beats the hell out of me.
Fastfwd, look closely at the detail shots. I see globs at each weld junction, not justthe outside edge (where they are more prone to pop). Also, look at the seat/ base connection on your chairs. There are a couple different versions, but not like the one in iuiu's photos.

A little hint
One way to tell the difference between a Knoll Bertoia piece and a reproduction is to look at the ends of the wires. Knoll flattens and tapers them to form a smooth finish where they meet the bar forming the frame. The knock offs don't have this detail, the wires are just straight cut. Knoll is now embossing the frame with their logo on the cross bar under the seat on the Diamond and Bird chairs.

Side chairs are stamped
Too.

So IMO
I would say these chairs are real, the wires have just been re-welded at some point due to stresses over time.

I will post tomorrow more...
I will post tomorrow more pictures, on the wire re-welded and the wire no re-welded, also the track to fix the seat to the frame (there is one).
By reading all the comments, i'm sure it's a real Knoll, It's just bad repair and had a few layers of spray paint over years. Some wavy wires and crooked are due by damage and the bad welded job. Like Pegboard Modern said, I don't remember seeing knock off in the 90th.
Maybe somebody have the real gauge size of the wires to compare.

Wire gauge
Current Knoll production uses thicker wires than on vintage chairs... But I don't know exactly when the change occurred.