Until a month ago all 3 of my kids shared a room. They are currently 7, just turned 4, and 19 months. ODD was 3 1/2 when DS was born and he slept in our room until 5 months old and then moved to the room with ODD so she would have just turned 4. Then when YDD was born she roomed with us until 8 months and then joined the older 2 in the kids room so they were 6, newly 3 and 8 months. They did fine.
Now we have 3 bedrooms so the 2 girls share. Ages 7yo and 19 months and 4 yo son has his own room.
The only time you should look in your neighbor's bowl is to make sure that they have enough. You don't look in your neighbor's bowl to see if you have as much as them.