Going with the theme your are trying to achieve, I would add a black leather ottoman to replace he white table. The built in shelf I would remove and sheetrock over it or paint in a matte finish black. Before you paint in black be sure your have accessories such as silver or reds to put in that space to set off the black background. You can put a series of pictures with silver frames or art objects of silver , red or combination. I love your table and chairs.

Its a really lovely room! what a great place for kids to share. I like kids sharing rooms. I think you need another colour to tie it together. I would suggest a blue tone.... teal, navy blue, duck egg blue. to tie it together. Its a little to pale and looks sparse, but actually isn't. I would leave everything exactly as is, BUT, paint the back wall behind the bed teal and find a simple navy blue wall decal that is fun and kid- like maybe one with a sillouette of a boy and girl playing. I would paint the wall behind the sofa duck egg blue. Then I think it would suit both kids more and look more kid friendly. the blues will balance the pink and cream, but because you have a pale carpet i don't think it will look too dark. don't worry about making it totally kid like, its a room they will grow with, not a kindergarten, and it also needs to peaceful and restful for sleeping. besides with their art on the walls and bright toys everywhere it soon looks bright and kid like. Good luck!

Reupholstering furniture is expensive. Do you think Red + Mustard or olive would be okay ? Should i add neutral colors in the place surrounding the sofas (like rugs, curtains, wall pieces) to minimize loudness? I'd flip this around. Go with neutral furniture - - bring color and texture in with area rugs, draperies, accent pieces...

Going with professional has its own advantages. Afterall he is pro, so he has studied more and has more experience. However is this person from the kitchen shoppee, which is giving you quotation of kitchen installation? In such cases, I have experienced that they just make boxy kitchens where they add lotsa fittings, that increases your budget. Open shelves does not need such fittings, so such are omitted...Normal door wali cabinets are less and number of drawers increased. Going on own is not a bad idea, provided you need to study it well. Note down the requirements, classify work areas and so on... In this approach , you have to go bit slower and carefully. Allow some flexibility in design, so that in future , you can alter as per the need. Sometimes we come to know the problems after few months/ years and we cant change it later. Ultimately compare between [your time+ efforts+ study+ error chances] Vs Hiring professional and go ahead accordingly.