Hey buddy, you might need to re-read what Amal answered above.
just to add a couple of points
xM1 is out of stock, unless you have an old one 
xM1 = High Frequency (HF)
Spark 2 = HF
xMagic = HF AND Low Frequency
NExT = HF AND LF
What Amal is saying here is, it is very difficult to target a specific implants with a reader when 2 or more implant of the “same frequency” (same protocol ie. ISO14443-A) are in very close proximity to each other.
so YES you can put them next to each other, but your reader will “decide” which one it reads first.
Best practice is to seperate them by distance / orientation / plane.
Right would be R0 = (P0 R)
Left would be L0 = (P0 L)
If this is the collection you are going with
Do you have a specific use case for them?
Anyway, heres my suggestion for the discretion you are going for, but in reality, it will depend on what you are trying to use them for and how fat your hands are or conversly how vascular your hands are
xM1 Unavailable
Spark 2 - I have a couple of ideas for this, but first, I need some more info; how do you plan to use this?