Your biggest limiter is 'hand launch at the local dinghy club' rather than using a car - trailer.
I do that. My boat is +/- 130kg without the trolley, and is on the limit up a ramp with a small lip on my own. I'm 46. As people get towards 60, that drops to 100kg up a ramp by my observation. If its a very flat ramp you could go higher, but thats not how they usually are.
While you may have crew to help push and pull, if you singlehand it, which you will, your boat's going to have to be 'suprisingly light' for its size.
On the good side you have alot of crew weight, which means intrinsically you can carry full sail in high winds, and have extra arms and hands to pull ropes, bail or steer, which is intrinsically sea worthy in itself and improve motion comfort. Also if you intend to leave your boat in the dinghy club park, you can infact have a stayed rig without penalty. While lugs are the rig 'du jour' currently, a stayed rig allows a jib on a forestay and the center of effort comes lower and helps to windward. With crew to pull ropes, I wouldn't discount having more than one sail too quickly.
If your weight limit is fixed, and it probably is if you also want to lift it into the rafters, from my knowledge of boats there are two that are 'alot of boat for the weight'. One is Welsford's Navigator, the other is Clint Chase's Calandar Island Yawl. Others that might come into range are Oughtreds Penny Fee and the Dix Argie 15. These can be built to 130kg ish. Your going to have to be sweating the materials - Occume ply, cedar and spruce maybe alloy spars. Stay off the hardwoods. Be 'economical' with epoxy, and no 'added extras' off plan. Be minimalistic. Be a 'less is more' guy. Think 'how can I make this item lighter' at every stage from planking, to blocks and sailcloth. Boat's with a planked bottom, and no keelson, save a little weight usually.
Otherwise many of the features cost weight and you'll need to trailer it in. Scamp has many of the features your looking for but weighs about 300kg as I recall, and thats at 12ft. A longer length to accomodate 4 people and the weight will be well into trailer territory. Scamp will sail 4 though and I wouldn't exclude it just because of its short length: its an 18ft boat without the pointy bits and has a nice character of its own. Exceptionally safe and capable. Short is also good inshore among moorings (or paying launch fees!). If you chose to trailer your boat in, and kept it on the driveway, then most of whats on your shopping list could be met with Scamp. Boats like the Vivier Lilou 2 has water ballast as does the new CLC Guider, Welsford Pilgrim and Long Steps.
Sleeping 4 is going to be difficult without heading towards 18-20ft length. Some of the demands on your list are conflicting. Going boating, requires making choices. You could even consider keeping a 20ft cabin dayboat on a drying mooring and building a hand launch 9 ft pram to get to it. Overall you might be best meeting your sailing objectives and adjusting your storage and launch solutions to cope with that. As someone mentioned above a Caledonia Yawl is a great family trailer boat. If your building something, your children will be bigger and heavier by the time your finished. Your combined weights plus the boat's weight plus a bag or two, needs to be the approx design displacement when your enquiring about a design. You want 6ft beam, freeboard, side decks (some people will be sat on the leeward side), foredeck, possibly a metal centerplate and an outboard well easily to hand. 10sqm solo, but with a family aboard possibly closing in on 15 sqm.
A Navigator will probably do it. Has alot of reserve stability. The standing lug main version will derig quickly. People arrange boards accross the fore and aft cockpit to sleep on it. It'd be a squeeze but you might find enough space overnighting, depends on how tall you all are.
