The answer is simple, you'll need 2 vSwitches for vSAN, one is your current vSwitch that are using vmnic0, let's say it's vSwitch1, and another is a new vDS that are using vmnic1 & vmnic2.
vSAN vmkernal is currently in vSwitch1.
You need to configure LAG for the new vDS, and add a new port group called vSAN-PG, set up VLAN id, set up failover order so the only uplink of vSAN-PG is lag0, vmnic1&vmnic2 is unused. In order to test all the configured is correct, you can add a test vm and let it use vSAN-PG, then setup a vSAN IP address see if the vm can connect to all the VSAN vmkernal addresses in cluster.
And last, do a vmkernal migration, select vDS, right click >manage Hosts>migrate VMKernel.
Thanks for the suggestion Dyadin.
After discussing it with VMware support, the solution was a little simpler, I just created a new port group, on the same DVS, that used the LAG as the active uplink and no standby adapters, and migrated the VMK of each host onto the new DPG....