Ever since they were foals.

@David Murphy  
Yah, they’re called the Amish, and people in loveless marriages

It was an old tradition to only connect the beds when trying to produce children. While this does promote self restraint, and maybe discourage unplanned pregnancies, it also encourages the idea that sex, just for the fun of it, is immoral. With the children on the other hand we don’t need to worry about babies from them sleeping in the same bed, and we require less beds if they have multiple sleeping partners. And thirdly this will decrease the chances of them freezing since all the siblings are sharing body heat. The opposite genders sleeping together is scandalous. Very few people are still this conservative, but I’ve seen examples.

That’s how you know the love is dead

Well it’s odd that the parents are separate, but the sisters were in the same bed because guests were sleeping in most of the beds. They probably normally slept in the two bunk beds that the Apples were sleeping in.

With a sleeping arrangement like that the fact that they even have one kids is a miracl, let alone four

Huh. Didn’t notice that.

Parents can’t sleep with children in beds because children needs to sleep in their own bed, same goes with their parents.

It’s funny how in the first one Pinkie wakes with glee, scaring Marble and Lime, but Maud…
 
Sleeps like a rock.
 
YYYYEEEAAAAHHHH
 
Also that family looks really depressing. Poor Pinkie. I’m really glad she’s at Sugarcube Corner now…
 
@Darth Sonic  
I know that feel.
 
Luckily modern mattresses can be quite amazing, so a compromise can probably be arrived to. And plus, some things are worth sleeping on a good but imperfect mattress for.
 
CUDDLES FTW!
 
Also it’s kinda funny to see that comment set to that profile picture :p

@Darth Sonic
 
Ah yes, the Hays Code… The same rule that forced Betty Boop to cover up XP

@Background Pony #E673  
That was only after the Hayes Codes.

They used to do this in old movies… They’d show a married couple in separate beds because they thought it was too scandalous to show them sharing a bed, even if they aren’t… ahem

After these four kids, they don’t want anymore.

@Red Cedar  
That makes sense. when my family have visitors over, sleeping rooms are switch around. mom and dad end sleeping in different room.

The thing I’m mainly seeing is the insane happy engine that is Pinkie Pie.
 
Look at that smile in the lower pic. So adorable.

@K9Thefirst1  
I just hope I never have to sleep in a different bed then my hypothetical wife. Removes a lot of the intimacy and romance for me. :(

Igneous and Cloudy already had Maud and when they were expecting Pinkie Pie to be born so they bought/bild extra bed. But Marble were born too, so they gave their big bed to their three (later four) kids and take two smaller beds for themselves. Why? Because they are good parents I guess.

It’s also probable that Igneous and Cloudy have different sleep needs: One needs a firm mattress and the other a soft one.
 
And it’s not THAT unusual for some couples to not only have separate beds, but separate ROOMS. It’s not due to marital issues, in these situations it’s due to either the couple each have widely different sleep/work schedules (one works the day shift, the other the night shift), or snoring is a major issue.
 
And as even a quick look through the “sex” tag shows, you don’t strictly need a bed to make Sexytime.

@Red Cedar  
Heh. That’s actually what a few people have been saying here in the comments :p

@Background Pony #7C2D  
Eh, I geuss its just that the show itself seems to project Liberalism, and I just projected that on Equestria itself? IDK

I noticed. My theory:
 
The Apples took the four bunkbeds formerly used by the four Pie daughters when they were growing up, so that they could be comfortable during their stay.
 
The four Pie sisters took their parents’ bed so they all had room (somewhat) to sleep.
 
Igneous and Cloudy took the beds currently used by Limestone and Marble, since they are the only two of the four sisters who still live on the farm full time.
 
Yes, I spent time considering this.

@Darth Sonic  
“Love is in bloom” hints that there’s no such thing as divorce in Equestria, they’re ruled by a divine monarch, and higher education seems mostly caste-based.
 
Not sure where you got that idea from.

@Cirrus Light  
I’d point out that Equestria seems like a fairly liberal society, what with the slight socialist overtones that come from Cutie Marks. That said, the Pies seem fairly conservative, so I gave you that.

@ED-SKaR  
So it’s built on a strong foundation? Xp

@ED-SKaR  
Badum-tsh!