Fish buying help!!! Dh? water hardness?

Okay so y'all may have gotten my previous question and thank you so much for your generous answers. Now i have narrowed it down to two fish, The platies, and The neon tetra. All the research i've done has shown that they like the same food, ph level, they are in the same water temp range, etc. The only thing is they like the water hardness (dh) different from one another. The tetras like a dh in the range of 1-2 and the platies like it from 10-12. Is this something to worry about? Will one be able to tolerate a higher or lower water hardness? Will they beable to survive in like a range of five? If you guys know any more differences between them let me know. And give me more (fresh water) fish ideas!!!!