Based on what I now know about the devices this configuration should work:
Ubiquiti equipment ISP 98.xxx.xxx.xx ---
Modem 10.1.x.x ---> (IPs?) NAT 10.1.0.1/30 to 10.1.0.2/30 (on the Ubiquiti router)
Ubiquiti Router (IP/etc?) ------> (IP?) Double NAT with Ubiquiti router in the Modem DMZ should work as I have used that configuration many times without issues. As for IP addresses, assign the inside interface 192.168.254.1/25 and assign IP addresses to the homes so they each have their own dedicated subnet. You could do this with subinterfaces on the Ubiquiti router or VLANs (whichever it supports), with one subinterface or VLAN per home serviced. Then on each subinterface or VLAN you dedicate a /30 subnet to a home which will require 4 IP addresses per home for each subnet (one for the network IP, one for the broadcast IP, one for the router's subinterface or VLAN and one for the home). So the first home could be:
192.168.254.4-7/30 and assign the VLAN .5 and the home .6
192.168.254.8-11/30 and assign the VLAN .9 and the home .10
and follow the same pattern for all 30 homes.
Since 30 x 4 = 120 and the router subnet is /25 (good for 128 IP addresses) the router's subnet mask includes the router's internal IP address is a "supernet" of the IP addresses assigned to the homes so the router can forward traffic to the router and each home has their own separate Internet IP address with routing disabled between VLANs.