You are not obligated to use an ad-hoc network with Lemur. Connecting through a shared network (i.e. through a router) is perfectly valid, it just means that latency will be a little bit higher (200-300ms on average, rather than 10-15 ms with adhoc). This could very well be acceptable for you depending on your particular use-case. Lemur can work in both cases.
Connecting your tablet (whether iOS or Android) to a Wi-Fi router is very simple. Go to Settings / Wi-Fi and select the same router that your computer is connected to. In most cases, this is actually already done as you might be using your tablet to go on the internet already.
Note: Many Windows users find it easy to use Connectify Hotspot software to manage their Wi-Fi and ad-hoc networks. Last time we checked, even the free version was well sufficient.
Once you are connected, you can now send/receive OSC messages or use the Lemur Daemon to send/receive MIDI.