If you are correct that your grandparents have a Ubee DVW325, then it's not just a cable modem, it is also a router and WiFi access point, so you should be able to utilise its built-in wifi capability.
DVW stands for Data, Voice, Wireless.
The specs for the DVW325 are:
- Cable: F-Connector, female
- USB: 1 USB 2.0 Host Port
- 8 x 4 Channel Bonding
- LAN: 4 10/100/1000 Mbps RJ-45 Ports
- 2 RJ-11 ports (telephony), PacketCable 1.5/2.0 Compatible
- DOCSIS 3.0 certified
- DOCSIS 1.0/1.1/2.0
- CE/FCC Class B, Energy Star Certified, WiFi Alliance Certified, UAPSD (power savings)
- Supports 8 WiFi SSIDs, 802.11b/g/n compliant with link speeds up to 300 Mbps, 2 Tx
SD