What should i get, 2 300's or 2 Fives?

The Era 300s are atmos capable speakers that fire audio primarily from the sides and top when used for surround speakers.  So placing them ~10 feet back of the seating area is pretty much useless at any volume. You may hear them from your seating area, but you will have lost the effect of having audio coming from the proper direction (bounced off walls and ceilings).

If you went with a ‘standard’ speaker, you can place them that far back and adjust by turning up the volume.  It’s not ideal, and audio will be very loud in your back area, but you can do it.   I wouldn’t spend money on Fives though, the new Era 100s should be plenty good enough for surround duty at half the cost.  I would also place the speaker near fridge on the other side of the stove.  It’s a better angle at that distance with less interference.

That said, you definitely are better off with rear speakers closer.  I get that you don’t want use stands, or a sofa table behind the sofa, perhaps due to lack of a near by electrical outlet.  Is there an outlet on the pillar?

As far as movie theatre sound and why it ‘works’.  First, they don’t bounce any audio off walls.  All the speakers are in walls and ceiling directly pointed at the audience.  Second, the speakers are above the seating area pointed down, so the seats near a speaker won’t be overpowered by the volume, but won’t hear as much coming from that audio channel.  Third, there definitely is a sweet spot in theatres where you’re going to hear the audio the best, as it’s intended.  If you sit on the edges, you likely are not getting the best sound and may not even be hearing some of the audio.  When setting up a home theatre, you want the sweet spot to be where you typically are going to sit.