Regarding the dining room:

Get rid of the table, buy a smaller round one. Round tables enhance togetherness and goodwill, eliminates hierachies etc. Make sure it's not a glass top. Wood is best... it creates "warmth". A central leg pedastle table instead of 4 legs is also best.

Consult a Feng Shui book. Depending on the location of the room, compass direction (which determines the quality of natural light etc) there will be differing suggestions.

An electric essential oil burner is a good investment. Burning citrus oils, especially mandarin and orange can make a room smell "happy". Cinnamon insense has a similar effect.

If you have a large plain wall without windows or doors consider painting this as a feature wall... plum, cornflour blue, a pale green are nice colours depending on the space/light etc. Dark colours will make it intimate and cosy... light colours make the space appear bigger (sounds what you might need). A large mirror could help as well but it's best placed beside or at right angles to doors/windows rather than opposite them. Often if you place a large mirror opposite a window it creates a silhouette of you as you look into it to see the room... hard to describe but I've seen it many times and it's annoying.

An eye catching light shade placed above the table... I like crystal chandeliers but the modern equivalent also really improves a space. If its directly over a table it can hang low. Other forms of indirect light like wall mounted lamps are great too.

Buy new artwork or a new floor rug. I love large textile (tapestry-like) wall-hangings. These work well near where people gather for meals because they absorb sound making the acoustics of the room nicer.