Check out Hotel Patritius - they have a Quadruple room and it includes breakfast. I stayed there in April and it's a nice location on a quiet street with very friendly staff. The price may be more than you'd like though - it's €288 per night for the quad room on a random night in August. Honestly, for a family room, this doesn't seem like a terrible price.
Years ago we stayed at B&B Dieltens (now named Amaryllis Dieltens and looks to be a different couple running it), but it was in a great location and the included breakfast was amazing. I couldn't find prices on their website, but you could email them. They don't have a quad room, so you'd need to get two separate rooms.
Good luck!