Running them in parallel makes for a lot more plumbing. You would need to split the supply line with one of these Y-manifolds, then route the hoses to the inlet side of each cooler. Then each cooler outlet hose would have to run back to another Y-manifold that merges the two outlets into a single return hose.
http://www.petersonfluidsys.com/plumb_yman.html
The 911 oil pump is pretty robust, especially your 930 pump, and you should have no problem running the two coolers in series.