LEAP 15.1 Create separate bridge with public ip nat.

Hi, i been struggling with this now.
host machine using `public_ip_1 `
host machine have access `public_ip_2 public_ip_3 public_ip_4 `
host machine will have `vm_1 vm_2 vm_3`
WANTED RESULT;
custom private bridge that will be used by all `vms`, and uses `public_ip_4 for nat`.
any help appreciated.
Thanks.