You need to remove every hose and flush out every section you can separately to make sure all the sand is out. After that remove the engine drain plugs and run the engine on the hose with plugs out.
Then do teh same on the other engine. Even though you think its fine, You will most likely have quite a bit of sand in it as well.
It sucks to do, but you'll be better off to get as much sand out as you can now.