Nighthawk R8500 guest network seeing devices when disabled

> [...] my work laptop can see devices on my home network. [...]

   Your (unspecified) "my work laptop" is connected to the R8500 using a
"Guest Network" SSID?

   "see" _how_, exactly?  As usual, showing actual actions (commands)
with their actual results (error messages, LED indicators, ...) can be
more helpful than vague descriptions or interpretations.

> [...] No matter what I try, [...]

   Think, for a moment, about how little useful information that
non-description conveys to the non-psychics in your audience.

> [...] Any thoughts on how to solve this?

   Depends on what you wish to "solve".  Is your complaint that
something like "ping" works between guest and non-guest devices, or that
some actual data-carrying service, like, say, file sharing, works
between guest and non-guest devices?

   On these routers, a "guest network" is not a separate network, but
there are firewall-like rules (enabled by default) which can limit the
ability of "guest" client devices to communicate with non-guest client
devices.  If you expect absolutely no communication between guest and
non-guest devices, then prepare for disappointment.