Tyre/Tube Sizes?

WisePranker

I've got a set of Specialized Nimbus hybrid tyres that I'm wanting to fit to my Pinnacle to use for commuting. The tyres are 26x1.50 and were running with 26x1.25/1.5 Presta valved tubes. My Pinnacle wheels run Schrader valves so I can't use the thin tubes with these wheels.
Can I run the Nimbus tyres with 26x1.9/2.125 tubes or will this cause a problem?

Also, what pressure should I run the Nimbus at?