For the first question, the answer is 'yes'. The router will work, but only the networks in the routing table will be accessible. For everything else, you'll get a "destination host unreachable".
For the second, if you have two (or more) overlaping networks, the longest-prefix-match will be used.
So, if you want to access
126.96.36.199, the second route will be used (doesn't matter in your case, since both use the same gateway), because the the match is longer (more bits match the network ID/mask).
If you have:
10.0.0.0/8 via gw1
10.0.0.0/16 via gw2
10.0.0.0/24 via gw3
10.0.0.0/30 via gw4
and want to ping
10.0.0.1, the packet will go via
gw4, since it matches more bits with the network id/mask then other routes.
is not a valid route (if you use /28,
188.8.131.52 is a network ID). However
184.108.40.206/29 is a valid route.