A floor plan would be helpful.

I agree with divadeva. More lights. If you can add pot lights do it. If they're already there add task lighting and up the wattage on the bulbs on the pot lights (replace with LED and you can make them brighter because the wattage on LED is lower for brighter light). If you have all of that add decorative lighting. If ventilation is an issue find a way to move the air around or add air filtration. Maybe the HVAC is deficient. Maybe you can add a HEPA filter instead of the standard one that comes with the unit. Call an HVAC specialist to see if there is a way to boost air flow in the room.

For the living room, the focus should be the balcony area. So flipping the couch to face the wall and not the dining table will help. Kind of like this pic. Even if you already have the sectional that is in the diagram, you should be able to flip it. In fact a sectional would probably work better than the couch in this pic. I also really don't like the style of this pic, but it showed what I meant, For the girls' room: No matter which bedroom you choose, you should maximize floor space so that they have the biggest play space possible in their room (as they get older you can add desks for school work and such). To get this space, I would give them bunk beds. This configuration gives them an open feel and more storage, essential for girls. You posted two different kitchen designs. This makes it hard to give you advice. I agree with other posts that your sink should be away from the wall. This allows you to have stuff to the left of you (drying dishes in my house), while you wash vegetables on the right of the sink. You need the same space on both sides of the stove, also. At least 24 inches on both sides is good. 36 is better, though. The first design has a nice little countertop space that adds a place for your daughters a space to sit a watch/ talk to you while you're in the kitchen. When they added this to the first design, you lost cabinets on the other wall. This is bad, as the space is already storage limited. Try making the rounded countertop bump out into the living space more. If you play with the shape, you could make it work without losing the cabinets on the other side. It doesn't have to be rectangular or a perfect circle. You can see how this one isn't confined to the floor plan of the kitchen. I think this is what you would need to do to make it the most functional.

What is the dimension of your bathroom? Looks like 4 feet wide, can't make out on length though. Glass partition or tiles partition for shower would help to keep your bathroom clean and dry and revamp look drastically. Wall hung WC is must, again from cleaning and look perspective. If window is not providing any light ( though your photo suggests some light coming from window) this area can also be used for multipurpose. You are welcome for more queries. Tiles selection can be decided based on a theme as well.