Very frustrated with this service. We were told we could use up to 8 devices at a time. We can't even use one!
We had no porblem using our Roku device before we got hughsnet! Now, we can't watch anything without it buffering 50 million times. This is our current problem.
Unfortunately, the latency with satellite internet can never be lower than about 600ms, and for most it usually ranges between 600ms to 700ms. Still, people are able to stream with various devices, including Roku.
One of the possible solutions is disabling Interference Mitigation in the Roku. You can see how to do so here. It's in the latter half of the post.
As well, it may help to turn off, or pause, the Video Data Saver.
Depending on what you are using the devices for, it's possible to use eight devices simultaneously, but if they're doing anything data intensive, it will likely be too many. The available bandwidth will be divided between each device actively being used, though not necessarily evenly.
Also, during the evenings, especially around the holidays, you're likely going to see considerable congestion, as the system only has so much bandwidth available. The more people actively using the service at the same time, the heavier the congestion will be, which can cause problems with things that require a good amount of bandwidth, like streaming.
BTW, how are you measuring the latency? If you have a computer, running a trace route or a ping to various sites, including the Roku servers, is the most accurate method for doing so.
If none of this helps, you may need to run some speed tests to demonstrate your current speeds, as low speeds can cause issues, as well. The instructions for the speed tests are here.
Lastly, please ensure that you are not out of data. When out of data your speed will be throttled, and normally to something under 3Mbps, though it can be as low as, or even lower than, 1Mbps.