There are a bunch of options most are kind of complicated. As mentioned here before ventoy will get clonezilla running from a network boot. Without clonezilla, a few things I can think of are:

#1 just clone the system while it's running. Get a large external drive and sudo dd if=/dev/your_internal_disk of=/path/to/disk/image.img

If you want you can boot into single user mode to do this, it's will be less risky and you may be able to mount root read only. Note that this carries no risk for the source machine if dd is used correctly, only that the filesystem of a target machine may have to be repaired after the clone.

If you'd rather just clone partitions that would work this way as well.

The target machine would need a live bootable is to copy the disk image onto the target disk. Dd is a inefficient option but it's on almost every system. Use partclone instead of you can, same as clonezilla uses.

#2 expose your disks with network block devices. You'll need kernel support I think, but then it's basically the same as #1 but you can do the clone from a remote machine

#3 build empty filesystems on the other machines just copy all of the files. You can use nfs or samba but it would probably be better to tar everything to preserve file ownership and permissions using these protocols. Rsync would probably be best. after copying the files a bootloader would need to be installed and configured.