premium user...

[chet05]

i have two (2) realms in one (1) account, what if i buy diamonds it is possible to share those purchase diamonds to use in both realms? and  how can i purchase/buy diamonds, where should i pay and is there a chance that i might get scum?

[Muwe]

http://prntscr.com/2f85t4

This is how you can buy diamonds.. and in my experience so far, the online shopping platform used is quite safe..
After you buy the diamonds you have to click here in your empire ( this will be visible after you finish the tutorial in  the begining) http://prntscr.com/2f86ha and click then, here: http://prntscr.com/2f86pu . In the Diamond Transfer box, you can share youre diamonds between the two or more realms you are playing..

[Madzoism]

Purchased diamonds can be transferred between worlds, you can buy them from here http://prntscr.com/2f92xh and there you will find Diamond Transfer tab as well. As long as you buy from here there is no way you will be scammed (and i don't think you can buy them from any other place) just choose your payment method.