Is it possible to send UDP stringer to multiple IP addresses at the same time?

Yes, this is possible.  The user manual describes it like this: (System > Show Control)

String TX IP Address

Sets the destination IP address that the console will send UDP strings to. Multiple IP addresses can be entered, separated by either a space, comma, or semicolon. Port numbers can also be appended to IP addresses with a colon to send UDP strings specifically to that port (10.101.2.99:8001, for example).

The same is true for OSC TX, described further down that page.

Yes, this is possible.  The user manual describes it like this: (System > Show Control)

String TX IP Address

Sets the destination IP address that the console will send UDP strings to. Multiple IP addresses can be entered, separated by either a space, comma, or semicolon. Port numbers can also be appended to IP addresses with a colon to send UDP strings specifically to that port (10.101.2.99:8001, for example).

The same is true for OSC TX, described further down that page.