Is it possible to put one RCD on all consumers?

Good afternoon, it is unclear what you want to do, "to protect the boiler in one group ... the rest ... in other groups." What do you call groups? Do you mean to put 1 RCD on the input and connect all the automatic switchboards from it?

It is possible, only then the RCD can operate false due to leakage currents caused by the total length of cable lines and consumer leakage.

In this case, it is necessary to increase the rated current of the RCD, not by 30 mA, but by 100-300 mA, and this is already a RCD not for protecting people, but for another, this RCD is called "fire-fighting". Therefore, if you want to save money, then either put one common RCD and differetomats on powerful and wet groups, i.e. to the boiler, stove, water heater ... Well, the oven. But not all at once, but several.

You can use a bunch of RCDs + an ordinary machine instead of dif.

That is, you can make group RCDs and power several consumers from them. For example, 1 total for 100-300 mA, then separately 1 differential or RCD + AV for the boiler, 1 joint for the stove and oven, 1 for the boiler and the washer. Those. in one RCD combine 2 lines. In general, the number of lines and consumers connected to one RCD is not regulated by anything. It is limited only by leakage currents along the line and in the device, which I wrote about at the beginning of the answer.