Binary comets, like 67P/Churyumov–Gerasimenko and MU69 Ultima Thule and at least a couple of others, have been observed. How likely would it be for a binary comet to again join with another object to form a trinary comet, i.e. three comets stuck together?
Could such non-destructive slow merger of comets explain extreme elongation such as that of the interstellar object 1I/Oumuamua? It might've been around for longer than the age of the Solar System, having time for more unlikely events. Is there a feasible process that lines up more than two bodies together?