You can keep CRS and RCS together but you might want to look into a buffering substrate like Fluval Shrimp Stratum or Azoo Plant Bed Grower. Both of those will buffer to about 6.8 (FSS 6.8-7) and both species can breed in that pH. You need to test the water first before you figure out which shrimp to go with. But if you have hard water, neos might be the only thing that will work if you're going to use tap and something inert like sand or flourite. And even then you have to watch pH and not let it get too crazy high (like over 8.4) So, learn about the different shrimps and different parameters FIRST, then figure out which way to go. A good site for just some basic info is
And don't forget to check the stickies at the top of the Shrimp Forum.