My lan currently has 2 pxe boot servers. One serves Ubuntu 18.04 via ltsp. The other serves pxe installers for a few linux distros as well as a Windows 10 installer. Right now these are controlled via the dhcpd.conf for isc-dhcp-server. That tells what to boot what via mac address.

My goal is to get everything to boot to the installer pxe server, then after a timeout move on to the ltsp server. Reason being is some of my machines pxe for linux, and have an ssd for windows. I'd like to just simplify my setup instead of having to adjust the dhcp server configuration file depending on what I want to boot.

Is this possible and how?

You can't easily chainload a nic firmware pxe from a boot loader but I think it can be done. Usually easier to use IPXE/GPXE. If I get your question that is.