You can connect to the powerboxes by mac-winbox (neighbors tab) even if they don’t have any IP (plug your laptop to any ether but ether1).
I assume you’re powering the powerboxes by their DC input jack.
To make the powerboxes plain switches:
1.- Reset both powerboxes, System > Reset Configuration, tick No Default Configuration
2.- Once rebooted, reconnect, and on both of them go to Interface > Ethernet, click on ether2,3,4,5 and set ether1 as their master port. You’re effectively creating a switch by doing this.
3.- Daisy chain powerbox B ether1 to powerbox A ether1.
4.- Plug the UBNT and any other antenna to any port on any powerbox, you’ll have 8 ether ports capable of supplying POE power..
5.- If you set IPs on the powerboxes, you should do it on top of the master interface (ether1).