First, always buy more material than you need as matching tints and dyes from different lots is a losing proposition if you run short.
Second, to answer your question accurately requires many more pieces of information than you supplied.
For example, are you interested in a single, uniform color without pattern? If a pattern, then you need to know whether the pattern itself runs along the width or length of the bolt; plus the repeat distance. Will you be doing all sides in the same material? Do you want plain seams or welting/piping, etc. Are you looking for a modern, contemporary look or tufted with matching buttons, etc.?
It would also help to see a picture of the particular couch and/or dinette (& dimensions) to better understand your particular scenario but since it isn't nearby...
To cover the basic variations, assume 6 (plain) to 9 (patterned) yards at 54" or wider for the couch and the same for the dinette as a starting point. Add more if you want piping and enough to make pillows, etc.
Personally, I have gotten away with as little as 5 yards for a couch while using my scrap/leftover pile for various elements and scrimping but I would not advise choosing that little without actual measurements.
"Good judgement comes from experience. Experience comes from bad judgment."
Sirs Gawain & Galahad
Air #48582, S/SO #003, WBCCI #4584