Is there any easy way to mount multiple single gang low voltage panels in a multi-gang box?
Standard approach is to use "Keystone jacks" (for whatever type of wire connection - there are all sorts.) and slot them into a plate that takes them (up to 6 will go in a single-gang box, with the right cover, double-width with 12 holes are common, 1, 2 or 4 for a single-gang is also common.)

A picture (or several) would help to inform further.

Presumably you have 2X Cat5e or Cat6 (house network), one coaxial cable connection (Comcast), and one phone line connection, given your described service providers and assuming that "AT&amp;T's modem" is a DSL so that it would be connected to a phone line. If that's not the case, there are probably still keystone jacks for whatever you have - you may even have some keystone jacks in single-port plates that could just be moved to a multi-port plate.