Hi @PhilG yes, you can order hardware and licenses using two different email addresses for your own billing purposes, and you may claim the hardware and licenses into the same Meraki Dashboard organization.
It might also prove helpful to make sure you define both of those email addresses as organization admins on the Organization > Configure > Administrators page. The important thing is not which email address was used for ordering/shipping, but simply that you use one of your Meraki Dashboard administrator accounts to "claim" the order number into your organization on the Organization > Configure > Inventory page. Then you would have a network defined for each of the two sites and place one MX67 into each network. You can create a new network also under the Organization > Configure menu.
As Ajit also mentioned, you will need to purchase the same license levels for both sites, because the Meraki licensing exists at the Organization level, not individual networks. So if you need the Advanced Security license, then the entire Meraki Dashboard organization would be licensed for Advanced Security, so then for two sites you would purchase two MX67 appliances and two Adv Sec licenses.
If you were going to configure the pair of MX67 appliances as an HA pair in the same network, then you would only need one license, since it would be an active/standby failover pair and only one appliance would be active at any time. But in two networks you do need two licenses, and they need to both be the same level (Enterprise, Advanced Security, or SD-WAN). Here is the documentation on the different licensing levels: https://documentation.meraki.com/General_Administration/Licensing/Meraki_MX_Security_and_SD-WAN_Lice...
Hope that helps.