MacBook – connect a firewire device and an HDMI display to 2015 Macbook Air with a single Thunderbolt 2 port

Since Thunderbolt is based on PCI Express, it appears that it is possible to connect to multiple hosts using the PCI express standard. However there may be additional software or hardware required to do such bridging of multiple hosts sharing multiple devices, whether this is true on Thunderbolt or not is not clear.

Things to look into are Non-transparent Bridging of PCI Express and subsequently Non-transparent Bridging of Thunderbolt.

PCI Express and therefore Thunderbolt are both peer to peer interfaces just like FireWire so thats a plus. However PCI express appears to have some host specific needs according to PCI Express Peer-to-Peer Interconnect from GE.

Its low latency, high bandwidth, widespread support and costeffective silicon have made PCI Express ubiquitous. It can however, be used for more than merely communicating between a host and a peripheral: it has many advantages as a peerto-peer communications technology. Enabling this, however, demands an understanding of how PCI Express works. This paper outlines the complexities that need to be understood and overcome – and describes a GE software product that delivers a solution that masks those complexities from developers.

As of now the only thing that Apple has defined for connecting two Macs via Thunderbolt is Target Disk mode running over it.

I have recently run into a similar situation as yours. Both of the proposed solutions below do not use expensive gear like thunderbolt docks or monitors, and can achieve the same (or similar) desired end result.

1. This Thunderbolt-to-Dual-HDMI adapter allows your to connect two 1080p monitors to a single Thunderbolt port, and have both those monitors act independently from one another (ie. they are not mirrored). The adapter is also passive, which is nice.
2. Buy a Chromecast. This solution is sub-optimal, and is dependent on you having a decent internet connection, but with this $35 device, you can stream a browser tab, your desktop, audio, video, and more to an external monitor. The third monitor can then be added with a simple Thunderbolt-to-HDMI adapter.