Sample1.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "HelloWorld.h"
#include "Sample1.h"
#include "Sample2.h"


// Sets default values
ASample1::ASample1()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

// Called when the game starts or when spawned
void ASample1::BeginPlay()
{
	Super::BeginPlay();

}

// Called every frame
void ASample1::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );

}

Sample1.h

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "Shared.h"
#include "GameFramework/Actor.h"
#include "Sample1.generated.h"

UCLASS()
class HELLOWORLD_API ASample1 : public AActor
{
	GENERATED_BODY()

public:

	// Or TWeakObjectPtr or whatever
	ASample2 *two;

	// Sets default values for this actor's properties
	ASample1();

	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

	// Called every frame
	virtual void Tick( float DeltaSeconds ) override;



};

Sample2.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "HelloWorld.h"
#include "Sample2.h"
#include "Sample1.h"


// Sets default values
ASample2::ASample2()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

// Called when the game starts or when spawned
void ASample2::BeginPlay()
{
	Super::BeginPlay();

}

// Called every frame
void ASample2::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );

}

Sample2.h

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "Shared.h"
#include "GameFramework/Actor.h"
#include "Sample2.generated.h"

UCLASS()
class HELLOWORLD_API ASample2 : public AActor
{
	GENERATED_BODY()

public:

	// Or TWeakObjectPtr or whatever
	ASample1 *one;

	// Sets default values for this actor's properties
	ASample2();

	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

	// Called every frame
	virtual void Tick( float DeltaSeconds ) override;



};

Shared.h

#ifndef ASample2__HEADER
#define ASample2__HEADER
class ASample2;
#endif

#ifndef ASample1__HEADER
#define ASample1__HEADER
class ASample1;
#endif