Please help me i don't know what i'm doing wrong.......................
It appears that you have a different def g/w on the 2nd client...hard to see the scrn shots to be sure, but it looks like 2001:2b8::.
Also, I would expect the def g/w to be 2001:db8:1234:: for both clients.
IPv6 GUA usage is different than IPv4 with public/private addresses. On IPv4, if the def g/w is not online, but the hosts are in the same subnet, they can find each other.
In IPv6, if you are using the GUA/ULA addresses, then the def g/w -must- be online, as the hosts actually goto the router even if in the same subnet.
btw, I would not use ::0 addresses in a production config and not even for lab. It is perfectly fine to do so and will work, but if I simply indicate this "2001:db8:1:1::/64" - is this a network prefix representation or a host IPv6 address representation. It's a little thing, but it can be confusing for some folks.
hth...Jeff
ps, a handy IPv6 cheat sheet - http://www.teachmeipv6.com/IPv6-Essentials-Cheat-Sheet.pdf