What special problems are there if I use two radio modules on the same board?
If you require concurrent transmission by one radio, with reception by the other radio, you'll need to evaluate how the Transmitter phasenoise or spurious will de-sense the receiver. Sharp transmitter filters (cell towers use these) and sharp receiver filter (ditto) permit lots of friendly concurrent activity.
The Transmitter phasenoise, however, should it overlap the receiver frequency, will de-sense.