The only thing you can safely keep with a crayfish (lobster) is rocks im afraid, they can and will eventually catch and eat any fish they are kept with.
Are you also aware that they are actually coldwater creatures that do best in temperatures of 15 to 20 degrees celcius? When kept at tropical temperatures (21-30c) it accelerates their growth causing them to shed more often which can lead to calcium difficiencies and weakness in the shell.
The ideal set up for a crayfish (lobster) is a longish shallow tank with a water depth of no more than 8 inches, decorate the tank with a gravel substrate and several large rocks and pieces of bogwood with at least one of them protruding the water surface, although they can live completely aquatic lives they do occasionally like to come out and bask on a rock.
Another popular myth is that they are completely carnivourous but they actually do better when fed on a mainly vegetable diet of peas, carrots and lettuce with meaty foods only being offered once or twice a week.