Is the issue that the bandwidth is being maxed out? i.e. issue not router buy how connection copes with lots of traffic
Given that people are probably watching iPlayer etc then this is the most likely solution, and general solution is
1. Rate limit individual connections, but with 30 rooms and 18 Mbps you end up so not one can stream video
2. Add more broadband capacity
3. Offer a two networks - free but slow and contended and a premium one offering say a rate limited 3.5 Mbps for a fee, and only sell 3 a day.
My suggestion is talk to the people at Solwise http://www.solwise.co.uk/wireless-hotspot.htm
and see what they recommend given the site of the property.