SSS- Tips

Paint the walls a soft, neutral colour. Shades that rarely clash with brighter decor are recommended. Colours such as cream, pale yellow, various shades of light blue, the right pale green, or even off-white are all good starting points.
If the children's' tastes are very different, a simple background helps themes coordinate. Plain furniture in similar styles, simple matching curtains, and a plain rug or flooring are all the large items that give cohesiveness. When all the larger items match, they allow the temporary contrasting themes or designs to rule.
In addition, having 'theme-less' furniture allows it to last past the first stage. Your kid won't like that Tonka Trucks toddler bed forever.
Once the foundations are in place, the rest is up to fantasy. Beddings, storage boxes, pillows and desk sorters are all fun and simple items that can be added to a room without clashing.
Even if the colours/themes/patterns are different, having similar sizes (such as storage boxes) or designs (such as bedding) can also add cohesiveness without matching.
if your kids don't want to split the room in two, or are too young to have a say, these ideas can still work. Keep the base colours and styles simple, and decorate with personalized pops of colour. This will prevent the nursery from looking too fussy or too temporary.

In terms of privacy, the older the children get, the harder it is to make solutions work. It depends on space considerations such as the size of the room, how much of the room can be made private, and whether the room is meant to be just for dormitory-style sleeping or for hanging out all day.
Semi-sheer canopy bed curtains can add a major privacy factor. Combined with a set of opaque curtains, (Caution note: These MUST be tied away before bed to avoid the risk of suffocation) you can give each child their own private domain for dressing.
Giving each child a cabinet with closed doors can help them keep their possessions feeling more private.
Create 'window walls.' You'll need a large blank wall, two corkboards, a curtain rail, and coordinating curtains. Each child can pin their own posters, artwork, awards and calendars on the corkboard, and when the other sibling's friends come over, draw the curtain to hide the girly pop band/gory truck movie decorations. If the curtains match the window dressings, few will think to look behind them.

Siblings Sharing Spaces- Solutions for Every Bedtime!