New customer, issues with latency with multiple users

[#1]

Hi there,
I'm a new plusnet customer, I've got the unlimited ADSL package, with an estimated maximum speed of ~7mbps however I generally average around 4mbps.
I use the internet for gaming quite a lot, primarily DOTA2 and I use teamspeak as my VOIP client. I have the issue that whenever one of my housemates streams video (youtube, netflix, iplayer etc.) my ping crashes from ~90ms with little variance to 2500+, essentially my connection is cut and the game is completely unplayable, often my connection to the teamspeak server also disconnects. This happens when using both a wired and wireless connection.
I spoke to an advisor and they simply stated that the the speed of my connection was not high enough, that streaming required a minimum of 2mbps bandwidth and even with prioritisation the performance of my connection with respect to gaming would be compromised. I don't quite understand this, as we are able to stream video on two devices relatively easily and in decent enough quality. It also confuses me that the connection to my game cuts out so rapidly, it's not that my bandwidth is reduced and the game lags a little, it just straight up dies, and as soon as my friend stops watching netflix it works again perfectly.
I have a feeling it is an issue with prioritisation as it seems like my housemates video streaming activities are seemingly not affected in any way when I play online game, DOTA 2 is not on the defined games list here: http://community.plus.net/forum/index.php/topic,444.0.html (although this hasn't been updated in a long while) and it wouldn't surprise me if TeamSpeak is not approved as a VOIP client either. I was going to run wireshark this evening and check the prioritisation, however I could be completely wrong about it all, is there anything else it could be? Is there anything else I can try to help improve my situation?
Thanks for your time and any help.

[#2]

TeamSpeak and DOTA are both in the traffic management system. However a speed of 4Mb/s is going to struggle if someone is watching YouTube (especially in HD) and trying to do other activities at the same time.
The estimate for your line is 5.5 to 7.5, so if you're seeing well underneath this then it may be worthwhile looking into. Can you confirm that your router is in the master socket without using an extension lead?

[#3]

Thank you for the quick response.
I've moved into a apartment which is the ground floor of an older house, I can't guarantee it's in the master socket however it is the most obvious socket in the main hallway of the property, is there a method of telling if you're using the master socket? 

[#4]

Generally they should look something like one of these: http://www.plus.net/support/broadband/master-socket-guide.shtml

[#5]

I'll check when I get home this evening, thanks!