Need help

Here's the loop() with indentation.

void loop() {

	if (digitalRead(B1) == HIGH && digitalRead(B2) == LOW) {
		digitalWrite(D2, HIGH);
		digitalWrite(D3, LOW);
	}
	else {
		digitalWrite(D2, LOW);
		digitalWrite(D3, LOW);
		
		if (digitalRead(B2) == HIGH && digitalRead(B1) == LOW) {
			digitalWrite(D3, HIGH);
			digitalWrite(D2, LOW);
		}
		else {
			digitalWrite(D2, LOW);
			digitalWrite(D3, LOW);
		}
	}
}

I'll try and write a testbed, and see what happens in the four scenarios:

This is what happens:

Condition: B1 : 0, B2 : 0 - D2: false ,D3: false ,D2: false ,D3: false ,
Condition: B1 : 0, B2 : 1 - D2: false ,D3: false ,D3: true ,D2: false ,
Condition: B1 : 1, B2 : 0 - D2: true ,D3: false ,
Condition: B1 : 1, B2 : 1 - D2: false ,D3: false ,D2: false ,D3: false ,

see how many times the same digitalWrite() is called, in  test 1, 2 and 4? 

Test code. The testLoop() is the same logic as your loop():

#include <iostream>
#include <string>

#define HIGH (true)
#define LOW (false)
#define D2 ("D2")
#define D3 ("D3")

bool digitalRead(bool value) {
	return value;
}

void digitalWrite(std::string pin, bool value) {
	std::cout << pin;
	if (value) {
		std::cout << ": true  ,";
	} else {
		std::cout << ": false ,";
	}
}

void testLoop(bool B1, bool B2) {
	std::cout << "Condition: B1 : ";
	std::cout << B1;
	std::cout << ", B2 : ";
	std::cout << B2;
	std::cout << " - ";


	if (digitalRead(B1) == HIGH && digitalRead(B2) == LOW) {

		digitalWrite(D2, HIGH);
		digitalWrite(D3, LOW);
	}
	else{
		digitalWrite(D2, LOW);
		digitalWrite(D3, LOW);


		if (digitalRead(B2) == HIGH && digitalRead(B1) == LOW) {

			digitalWrite(D3, HIGH);
			digitalWrite(D2, LOW);
		}
		else{
			digitalWrite(D2, LOW);
			digitalWrite(D3, LOW);
		}
	}
	std::cout << std::endl;
}

int main() {
	testLoop(false, false);
	testLoop(false, true);
	testLoop(true, false);
	testLoop(true, true);
	return 0;
}

Now using beacon_dave's logic:

result:

Condition: B1 : 0, B2 : 0 - D2: false ,D3: false ,
Condition: B1 : 0, B2 : 1 - D3: true ,D2: false ,
Condition: B1 : 1, B2 : 0 - D2: true ,D3: false ,
Condition: B1 : 1, B2 : 1 - D2: false ,D3: false ,

Test code: The testLoop() is the same logic as Dave's loop():

void testLoop(bool B1, bool B2) {
	std::cout << "Condition: B1 : ";
	std::cout << B1;
	std::cout << ", B2 : ";
	std::cout << B2;
	std::cout << " - ";


	if (digitalRead(B1) == HIGH && digitalRead(B2) == LOW)
	{
		digitalWrite(D2, HIGH);
		digitalWrite(D3, LOW);
	}
	else if (digitalRead(B2) == HIGH && digitalRead(B1) == LOW)
	{
		digitalWrite(D3, HIGH);
		digitalWrite(D2, LOW);
	}
	else
	{
		digitalWrite(D2, LOW);
		digitalWrite(D3, LOW);
	}

	std::cout << std::endl;
}

Now using beacon_dave's logic:

result:

Condition: B1 : 0, B2 : 0 - D2: false ,D3: false ,
Condition: B1 : 0, B2 : 1 - D3: true ,D2: false ,
Condition: B1 : 1, B2 : 0 - D2: true ,D3: false ,
Condition: B1 : 1, B2 : 1 - D2: false ,D3: false ,

Test code: The testLoop() is the same logic as Dave's loop():

void testLoop(bool B1, bool B2) {
	std::cout << "Condition: B1 : ";
	std::cout << B1;
	std::cout << ", B2 : ";
	std::cout << B2;
	std::cout << " - ";


	if (digitalRead(B1) == HIGH && digitalRead(B2) == LOW)
	{
		digitalWrite(D2, HIGH);
		digitalWrite(D3, LOW);
	}
	else if (digitalRead(B2) == HIGH && digitalRead(B1) == LOW)
	{
		digitalWrite(D3, HIGH);
		digitalWrite(D2, LOW);
	}
	else
	{
		digitalWrite(D2, LOW);
		digitalWrite(D3, LOW);
	}

	std::cout << std::endl;
}

that seamed to fix it. thanks for the help

You will still have to work on debouncing the buttons. The loop is run many many times per second, and a mechanical switch doesn't nicely open or close at once. It bounces up many times very fast, before permanently open or close the contact.

But the processor may be faster than those fast bounces, and your code would behave unstable because of that.

One possible easy option is to:

first digitalRead() all inputs at the begin of the loop in local variables. So that you don't poll the same pin several times in the same loop.
In your if statements, you then use the variables, where you now use the repeated digitalRead() calls

And put a delay(x) at the end of the loop, after all  the if statements.
Experiment with the x value, so that you don't get bounce issues, and that the project is still reacting.

delay(20)  would be a reasonable start point for experimenting.

#define BUTTON_1 (14)
#define BUTTON_2 (15)

#define DEBOUNCE_DELAY (20)

loop() {
  // poll input state at start of the loop
  bool btn1 = digitalRead(BUTTON_1);
  bool btn2 = digitalRead(BUTTON_2);

  // execute logic based on the gathered state
  if ((btn1 == HIGH) && (btn2 == LOW)) {
    // ...
  }

  // debounce delay (not the best debounce method, but may work)
  delay(DEBOUNCE_DELAY);
}

thanks the delay made my motors to start better

For debugging you could add big delays (like 5 seconds) at the bottom of each if/else block, so that after a button press it stays with the outputs you set, so then you have time to test them. Combined with the Serial.println, that should give you a fair bit of extra insight into what is happening.