All of these "tutorials" are obsolete. (Note they can still be used if you want to use the older style of manual configuration, but this requires detailed knowledge.)
If you are running a recent Raspbian /etc/network/interfaces should be as below. If you have changed it PUT IT BACK.
iface lo inet loopback
iface eth0 inet manual
iface wlan0 inet manual
iface wlan1 inet manual
/etc/dhcpcd.conf as follows (extract from
Configures a static value. If you set ip_address then dhcpcd will not attempt to obtain a lease
and just use the value for the address with an infinite lease time.
Here is an example which configures a static address, routes and dns.
PS I still think setting up a static address is almost always the wrong thing to do. If possible set a static reservation in your router (if possible) or use a
zero-conf such as