Nothing a 74HC4052 won't fix perfectly easily! 
Connecting an analog multiplexer and drive it properly is another side job.
@alaminrifat may try with the following 4051-based single-ended network if it works?
If the ESP8266 hasn't been purchased yet, then an ESP32 has multiple ADC channels and more pins available.
Quite so. 
Where did PighiXXX go?
I have 2 int variables and 1 float variable. So, What code should be on my sender and receiver side?
What is your setup -- Node, UNO, and UART or
ESP32, UNO, and UART?
See I've Done my project -
Here is my GitHub project repo - https://github.com/alaminrifat/water_monitoring_IOT
You can give suggestions to optimize the code.
Thank You and everyone for your help.
Q1.
Why have you initialized to an integer value when the declared variable is float-type?
float temperature , tdsValue = 0;
Q2:
The value is already in float and yet why have you casted it to float?
float phValue = (float)avgValue * 5.0 / 1024 / 6;
Q3.
Why have you inserted pair of double quotes when you are printing only a single character?
Serial.print("A");
Q4.
In the for() loop, why have you not placed the sub-ordinate clause within pair of braces?
for (int i = 2; i < 8; i++) //take the average value of 6 center sample
avgValue += buf[i];