Hoping someone can help with a little advice.

First a little background info:

Router: Draytek Vigour 2820
WAN Connection: ADSL2+ exchange less than 500yds so getting maximum available

This router is being used in a holiday cottage that takes up to 4 people.

The problem being that I believe that access to the net may be being abused. This week being the worst ever insofar as 2 people have 8 devices connected and in the last 24hrs alone they have downloaded 108GB of data!
3 devices have been downloading continuously for the last 6 days downloading over 80GB a day.

ON Holiday!!!!!!!!!!!!!!!??????????????????????? I believe that guests are doing a lot more than checking emails, updating facebook etc etc

This concerns me, are these people downloading pirated movies, music and the like using P2P applications?

I know that at the mo many Windows M$ devices are downloading the Win10 upgrade but something else is going on here.

So how can I find out what's going on and can I use the routers bandwidth & Session limit settings to control / reduce abuse?

If so what would be a realistic set of data for:

Default Max Session Limit for my own laptop when I visit & two TV's using BBC iPlayer / ITV Player (Fixed IP Addresses)
Specific Max Session Limit for all other devices. (Dynamic IP Addresses)

Default Bandwidth RX & TX Limits for my own laptop when I visit & two TV's using BBC iPlayer / ITV Player (Fixed IP Addresses)
Specific Max Bandwidth RX & TX Limits for all other devices. (Dynamic IP Addresses)

Been monitoring my own access over the last few days and have decided on

Default Session Limit: 10,000 which will be shared between my laptop and two TV's.
All other users to have a limit of 175 each

Default Bandwidth Limits of TX (Up) 10Mbps, RX (Down) 20Mbps which will be shared between my laptop and two TV's
All other users to have a limit of TX (Up) 100kbps, RX (down) 2850kbps each

The BBC iPlayer downloads at 2800kbps

Tried these restrictions on myself (as a restricted user) and I can watch a BBC iPlayer program in HD and remain logged into my yahoo mail account and surf the bbc news website without feeling to restricted, just.