They may have used small dowl rods or biscuits to join the chair. Which usually means a void/rebate is created and then a proud piece glued into the void. (Think male/female sockets etc). So you may be able to gently tap (rubber mallet, not metal hammer) to get the pieces apart. Use fabric or thick wadding or sponge to protect your timber when you whack it.

I love sky blue and want to paint my room, so i think it depends upon choice and likeness

Love your style and you've got some beautiful furniture there! A deep aubergine purple velvet on your wingbacks would look stunning. I'd tend to stick to purples in this area to keep it classy. Also, a dark purple would be more practical with kids than a cream. I'd keep the chairs you've got, unless they are really wobbly. Get someone to check them out and give you a quote for repairs and then you'll have a price to work against to see if you can get cheaper. OnePlan is right on the style and yet I don't think they look out of place in the room. I also like the idea of bench seats or if you wanted something really different, you could get a church pew?! I don't think the room has too much dark furniture as it is a large light area. Keep us posted with pics/samples of possible fabrics you find. Also, check out fabric outlet places.

These chairs are easy to recover and the range of fabric available today gives you plenty of choice. I say go for it. If you don't feel up to it yourself get an upholsterer, but plenty of YouTube tutorials about.