question

I hope i get your question right, given the little information from your post. What i hope you're looking for:

You want to know if a Multiplus or Quattro device in the ESS (Energy Storage System) configuration (1 phase = 1 Multiplus) can power loads on the AC-Out (critical or so-called essential loads) AND feed back energy on AC-IN. The amount of power its supplying is measured by the EM24 (all 3 phases combined). Simply put: yes.

BUT

its only a "pass-through" kind of situation on the AC-OUT while Grid is connected. If you're trying to set-up a gridless Isle-type system, this won't work at all or will only work with another setup configuration. Im assuming you're not wanting a Gridless setup though:

Here a Picture of the setup we're talking about (ignore the other AC-coupled Solar or "Grid Inverters" they are only there to show what else is possible):

you can see the Transfer switch inside the Multi passes through Grid to Essential AC Loads. The Multi would simply try its best to feed combined Energy consumed (measured by EM24) back to the Grid, while always prioritizing AC-Out, as the essential loads first. If the Multi can't supply full Load on the Essential Loads on AC-Out due to low solar and/or battery, the Grid will feed the rest through the transfer switch up to its rated max Amperage.

In case essential Loads are fully supplied by the Multi, but other non essential AC-Loads are present in the House installation for example and lots of solar or battery power is still available, the Multi will try and feed back the measured amount of Power by the EM24 via AC-IN to the Grid on the phase its connected to. (this is not 100% accurate as you will have some measuring and latency errors making the netted consumption of all three phases in this case "around" 0W)

(Warning, there are some Countries that don't allow Grid feedback at all or just under certain conditions! In Germany max. Feedback rate in 1 Phase systems is 4.6 kW for example. Make sure to check in the Documentation and spec your setup accordingly, with all the needed Settings.)

In case of an Grid failure ONLY essential AC-Loads on AC-Out will continue to be powered via Battery. AC-In will be shut off by the transfer switch, assuring safe working conditions on Grid side / Installation side. It is not possible, as far as I know, to feed back energy to Grid OR to the non-essential Loads of the house in that picture, with no or not enough Grid Voltage present.

Things to look out for:

AC-Out Transferswitch capabilities: different Multiplus devices have different Amperages they can provide on the AC-Out Transferswitch. Look it up in the documentation and decide what you'd need accordingly.

Complete ESS configuration can be different, the full Documentation is found here: https://www.victronenergy.com/media/pg/Energy_Storage_System/en/index-en.html

See this helpful Brouchure to get to know the available Products and their differences: https://www.victronenergy.com/upload/documents/Brochure-Energy-Storage-EN_web.pdf

Be sure to look up the Manual on the Victron Mainpage to give it a read aswell if you decided that a Product is suitable for you.

This is a lot of assumptions I had to make, be careful if this applies fully to your specific Situation and recheck things in the Documentation I linked. A ton of things need to be considered to setup an ESS correctly, so take your time and double check.

Hope this helps!