I use Microsoft Chromium Edge windows 10 and the result is the most promising against using other browsers.
ONE instant Only of EA studio uses 40% of 8 cores (equally distributed)
M30, Generator

2 instances use about 60%

For one instant
Chrome uses 30%
Firefox 20%

Trade safe

Thanks a lot for your detailed explanation. Currently I use a VPS at Contabo, so I think they limit CPU use and I cannot change some configurations - I did try on the past with their support.

Thanks again!

Looking at your screen shot of 4 browser instances, perhaps consider:

1. If all 4 instances of Expert Advisor Studio are configured identically (same pair/instrument, same Data Horizon, same EAS configuration, I would think that Task Manager should show 4 CPU's having similar and higher utilizations than any CPU's beyond 4.  But, yours doesn't. Perhaps one or more EAS configurations are different?

2. I am concerned that Task Manager CPU information does not look as perhaps it should.  Your CPU, an Intel Xeon E5-2630 v4 has 10 physical cores and with Hyper Threading, is capable of 20 threads, but yours is showing "virtual processors 10" instead of what I would expect should be "cores 10, logical processors 20", plus a few other differences (for comparison, see my attached screen shot for a computer with dual Xeons).  My first guess is that you have a configuration problem somewhere, which might be affecting one or more things.

3. I wonder: is your computer BIOS configured to enable Intel HyperThreading, perhaps labeled "virtualization"?

4. If so, I next wonder if your Windows 10 is configured to boot normally?  Perhaps examine your settings showing in the msconfig utility, especially Boot tab, Advanced options button, and make sure Number of Processors option is not being used to reduce CPU core/thread availability.

For comparison, my attached screen shot is showing CPU Utilization (using Windows 10 Pro 1903), per your example, running 4 instances of EAS (using the Opera browser, which I think, should be very similar to Chrome), with 4 of the CPU's showing higher utilization than the others, as expected. Beyond that, mine shows information which yours does not: number of cores, logical processors, virtualization enabled, and amounts of L1 cache, L2 cache, and L3 cache (while yours shows N/A for all cache information).

I was able to check it on my machine  by starting and stopping EA Studio instances:

Anyway, even if they are in the same browser, each tab runs in own process, so the cannot run on the same core.

I am running 5 reactors on a 10 cores PC but it seems that all 5 reactors are running on the same core. Can someone confirm this? How can I make the PC split the reactors reanning between the cores?

Also, is Chrome the fastest broweser? Should I use something else?

Thanks a lot!

Jose