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Sensor1Serial.begin(9600);
Do not call begin() on every pass through loop(). Call it ONCE in setup().
Sensor1Serial.listen();
if (Sensor1Serial.available()>0)
{
You've just started listening. What do you suppose the odds are that data will arrive in the 62.5 nanoseconds between the two instructions?
You don't stand a snowball's chance in hell of listening to two software serial ports at the same time. Either get a Mega or forget this project.
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