There are few folding tricyles. The only one I can think of that would be suitable for hauling uphill would be the Carryme from Pacific Cycles. The smaller wheels would have some problem if the path was not well made, but could of course be easily negotiated past any bad bits as long as there aren't too many of those.

Other foldable trycycles would approach 15kg. I think Diblasi makes a 20" one.