Multiple xbox live accounts on same internet connection.

[#1]

Hi,
My eldest son uses Xbox live on our internet connection.  Now my second son has decided that he wants his own Xbox and he also wants to use it with Xbox live.  At the moment it's on his xmas wish list and I need to know a little more before I spend any money.  My understanding is that I will need to pay for 2 separate xbox live subscriptions even though it's going via the same internet connection, please confirm if this is correct.
The chances are that they will want to play against their respective friends at the same time, and maybe even on the same games against each other.
I need to know for certain that it's possible to run 2 Xbox live accounts over my single internet connection and what if any impact that might have on any other online activities that might be going on at the same time.  For example, I generally work from home at least one day a week and connect to my office network over a VPN.  I already suspect that Xbox live is grabbing a lot of the bandwidth and sometimes I've had to ask him to stay off-line while I'm working.  Apart from these our other usage is relatively modest, being mainly used for accessing email and web-browsing.  I do occasionally use P2P but this is infrequent and I try to do this late in the evening when nobody else is using the connection.
I use a 4 port Netgear DG834PN wireless router to connect to the internet and I run a cable from this to my eldest sons bedroom and also to our family PC.
I am thinking of upgrading this to a wireless-N router such as the DGN2000 because we have a few wireless blackspots in the house and I'm hoping to eliminate these by upgrading the router. I will retain hard-wired connections for the family PC and the Xbox's and use the wireless for laptops.
My current broadband product is the "Force9 Broadband Your Way Option 2" product. 
I'd appreciate any advice on what if anything I need to do to make this work and any potential problems I might encounter.  Also any thoughts about the router I'm currently using and the one I'm considering upgrading to.  Finally, whether I ought to switch my broadband product to something better suited to my current requirements.
Thanks.

[#2]

kdband,
I can confirm that you will need to pay for 2 seperate xbox live subscriptions.
I have previously run multiple 360s down one internet connection without any issues whatsoever - that being said, I am connecting at the full 8128kbps! What speed is your connection currently running at? (You can run a speedtest at http://www.mybroadbandspeed.co.uk).
I understand that Gaming is always prioritised on BBYW Option 2. Xbox Live shouldn't really hog the bandwidth, as it doesn't use all that much (however if you're on a "slower" connection, you'll notice it more). How much of your usage allowance are you currently using each month? Adding another 360 shouldn't impact it in a major way...
Hope this information helps, if there's any other information you need please let me know

[#3]

Hi SparckZero.  Thanks for the response and for confirming that I do indeed need to pay for 2 separate xbox live subscriptions.
I'm at work at the moment and I haven't run a speed test for some time.  I used to get close to 8Mb at our old house, but I know it was nowhere near that speed last time I ran it at our new address.  I might try a few times tonight to see what I'm getting.
Last month was a very high usage month for me, downloaded some large files from P2P, but still only got to about half of our 15Gb allowance.  That's not something I'm not overly concerned about really.
thanks again.