For multiple passengers, you absolutely need a trailer boat. There's just no way to meet that requirement with a cartopper and have even a basic level of comfort afloat.
And even with trailer boats, you need a big one for multiple passengers in decent comfort. To give you a couple of examples:
1.
Ross Lillistone's Phoenix III design (15' 2" x 4' 8" beam). This boat is WAY too heavy to cartop. It can carry 2 adults in decent comfort. It can even (snugly but pretty comfortably) sleep 2 adults on board. But adding a third person makes it feel crowded--ESPECIALLY if that third person doesn't know how to sail, so doesn't understand where to sit, when to duck the boom, etc.
2.
Don Kurylko's Alaska design (18' 1" x 4' 8" beam). This boat is WAY WAY WAY WAY too heavy to cartop, and far too long anyway. If you sail it as I do, without the mizzen mast and sail, it can be comfortable for up to 3 adults (one at tiller, one on center thwart, one way up in the bow facing backwards--very comfy). It can also (snugly) sleep 2 adults aboard. But really, the amount of usable space aboard is very similar to the Phoenix III, despite the longer length (which really only gets you space for a third adult in the bow).
The reality is, small boats are small. And even when enough "seats" exist on paper, there is rarely enough room or comfort (backrests, etc) to make them good people-haulers. And if you force people to accompany you in uncomfortable boats, you will quickly create non-sailors of them. I've sailed with 4 people in a 12' boat and no benches or seats. That works. For young people who don't care about comfort. For about 20 minutes.
So, you may need to adjust your expectations and approaches a bit... Not meant to be pessimistic, just my honest thoughts.