Notifier - send SMS over Arduino one + GSM Shield

I need to prepare a program for arduino uno and GSM sheald that performs the following functions:
1. when the digital input is contacted, for example PIN1 on GND (for at least 5 seconds - (adjustable 2-30 sec)) an SMS (alarm 1) is sent to the number (A), sending is repeated every 15 minutes until an SMS with the content OK comes from the number A.
2. when the digital input is contacted, for example PIN2 on GND (for at least 5 seconds) an SMS (alarm 2) is sent to the number (A), sending is repeated every 15 minutes until an SMS with the content OK arrives from the number A.
3. when the digital input is contacted, for example PIN3 on GND (for at least 5 seconds) an SMS (alarm 3) is sent to the number (A), sending is repeated every 15 minutes until an SMS with the content OK comes from the number A.
It is a simple actuation when triggering on digital inputs Arduino uno.
Conditions:
1. reliable operation
2. Use Arduino Uno board
3. use of version Arduino SW 1.8.20
4. use of standard libraries (GSM 900)
5. use of GSM shield - see picture attached
6. A and B number need to be configurable
7. Need to simple add aditional digital input for Alarm 4 (pin 4, ..)

attached is the library for sim 900

Is a simple for notifyer over SMS ...