Euclid has visible imager and near-infrared spectrometer and photometer. Webb is all infrared. So they have non-overlapping missions even when observing the same structures and objects.
Also space is very large. The L2 orbit is gigantic and the probes are teeny tiny in relation. So it's hardly crowded in any sense.
I'm sure crowded is far off, but it's still interesting to think how they interfere with each other's instrumentations (given the field of vision is immense in comparison to their size), is there some type of space control traffic involved?
The L2 point is about 1.5 million kilometers from Earth. The various probes like Webb and Euclid orbit around that point at (IIRC) about a million kilometers. The various probes in that orbit will effectively never interfere with each others instruments.
As for coordination, at that orbit, it's going to likely be the individual agencies coordinating with one another. Every probe/satellite launch gets COSPAR IDs and other tracking IDs through various national and international agencies.
Also space is very large. The L2 orbit is gigantic and the probes are teeny tiny in relation. So it's hardly crowded in any sense.