SBUF holds ONE character, you will never pass the second IF. You need read the characters to a buffer and then test or use a state machine such as (gramatically incorrect and incomplete, just showing the idea)


.. init
state = 0

ISR
if (RI)
{
switch (state)
case 0:
if (sbuf = 'J') state = 1;
if (sbuf = '0') joybutton= 0;
break

case 1:
if (sbuf = '1')state = 0, joybutton=1;


deafult:
state = 0;

Have fun,

Erik