Even though it's possible to create ae (aggregate links) in vwire links, the simplest straighforward way to configure what you need it's just negotiate tha aggregation links between you upstream and downstream switches, if they using LACP (layer 2) the vwire should just forward this packets and the AE will negotiate correctly between the switches.
Now in the PA configuration you only need to configure your links as single vwires and mirror the configuration between them.
The funny part is the asymetric traffic, you can mitigate some portion in the switches in the case they support symmetric LAG hashing (so that individual flows are "pinned" to a single virtual-wire) to avoid overload your HA3 link. Also be careful and use the same zones in the mirrored configuration: if you use "external-vlan2" for the vlan 2 in physical link eth1, use the same zone for the same vlan in the eth2.
Hope it helps,
Regards,
Gerardo.
... View more