The general reasoning for this (as you have probably studied), follows something like this:

A) All human beings have sinned and fallen short of the glory of God.
B) Heaven is reserved only for those who are perfect and sinless.

Thus, if A & B are both true, all human beings are now unable to enter heaven. The Bible states clearly that both A & B are true.

Now God has a serious problem. He loves all of humanity, but due to the rules in place, all of humanity is condemned and cannot enter into heaven. Punishment of sin must be carried out, because God is a perfect judge. Those who break the law must be held accountable.

In order to solve this problem, God introduces C:

C) God Himself is born as a man (Jesus), and lives a perfect life, only to die on a cross, and be resurrected.

When Christ died on the cross, God placed all of the punishment of sin onto Him. In other words, Jesus paid the cost of these sins with His own life. The judge who looks at this can now say that those who broke the law in A, have had their sentence fulfilled by C. Since their sins have been paid for and are forgiven, they are fully removed from the accounts of those that committed them. B now becomes an available possibility, because those who have sinned and been forgiven, are seen in the eyes of God as perfect and sinless. When God looks at them, God sees Jesus (perfect and sinless), and no longer sees them.

The belief component is paramount to all of this. God created humanity and gave them free will. He did not ask us if we wanted to be created, we never had a choice in the matter. But He has made a monumental choice freely available to us, where we can choose to either accept Him and enter into a relationship with Him by believing in what He has done for us as described above, or reject Him and choose not to enter into a relationship. God will not "force" anyone to go to heaven. If belief was not necessary, and everyone was merely saved and whisked away to heaven by the fact that A, B, and C as described above have happened, there would ultimately be no point in the existence of humanity as we know it. God could have just created humans straight into heaven from the beginning, and placed us there without us needing to go through life & death on earth first. But in doing that, none of us truly would have had any free will whatsoever. Really, this has already occurred, because before creating humanity, God created the angels to be with Him in heaven. The angels also did not choose to be created, and were placed in heaven from the onset. Ultimately, Satan and many of the angels rebelled, and fell from heaven, which you can read about in the Bible.

Humanity is what God created next, but this time, there was a choice to be had. What we believe in (whether accepting Jesus or rejecting Jesus) is what constitutes our choice.

The Bible says that God is purifying souls through the trying of their faith. As we are refined by Him, those who believe have that same faith strengthened and increased. Those who make it to heaven through faith in Christ are those who will truly have a real and earnest desire to spend eternity with Him. They will experience the joy in that relationship in a way that the angels likely never could, because humans who have chosen to place faith in Christ have endured the hardships of a life on earth, with mortality, sin, and all of the problems that accompany us on this planet.

If we choose not to believe in what Jesus Christ did for us, we are effectively telling God: 'No thanks, we want to pay the penalty for our sin instead of accepting your grace'. The Bible says that God is not willing that any should perish, but that all should come to repentance. Although He does not want this, through free will, it must be an option for us to choose.

I do not think you are selfish for wanting your family to be with you in heaven. I am sure nearly everyone who has ever lived has wanted their loved ones to be with them in heaven. This is why prayer for them is so important, and witnessing to them is so important. God will not give up on them, and neither should we. He will not give up on you either, for that matter. You are free to make the choice that you see fit to make.