Combine Multiple Modems to Form Faster Internet

So at our small business we have 3 AT&T UVerse modems. The IT person that we hired attached all three to a mikrotik rb1100ahx2 then has one Ethernet coming out of that connecting to a switch which has multiple Unifi APs.

Is it possible to combine multiple modems to form 1 fast internet line? How does IP address work?

Thanks