2 and 3 seater sofas

Depends on the condition. Your commune will probably come and take them away to the dump if you ask (but you may have to pay a small fee), or alternatively, there are groups like http://petitsriens.be/ or https://vincentdepaul.be that take second hand stuff and renovate it / donate it. You could also go along to your local church for example and ask there if they know of anyone who could need them.

you'll be surprised by what people take, just put a picture in websites like https://www.2ememain.be/ or search some facebook group pages like brussels for free and it will be gone in a couple of hours

Google your nearest troc and contact them to sell with out the hassle, but if you want to help others use petit rein as above great organisation for taking unwanted items Andy I think they will pick up larger ones like sofa

When I replaced my sofas, the company who delivered them took them away. Don't know what they did with them.
Are there any 'battered wives' homes where women and children are taken for their protection, in your area? I have given furniture and furnishings to them in the past.

https://www.dwump.com an app to dump in brussels. post what you need to dump & set your own price, if item has a value set price €0