When my father died I asked myself, 'is he really my dad?' Yes, biologically he was without doubt! But, now that he resides spirit-side, an entity of the one creation, originating from the Source just like myself – it's clear that on a spiritual level he didn't spawn my existence. Only on a human, physical, or biological level was he the catalyst for my creation. So instead of being my father, he is instead likely my companion, friend or contemporary. We may be of a similar cosmic age – if time even really exists in the universal realm. Hence, the perception of communication with my father through prayer, meditation or a medium fell away. Now he's an important, much loved, friend or companion.
Reincarnation cases have been recorded worldwide involving recently deceased family members reincarnating as new family members, friends or acquaintances. Examples exist of individuals reincarnating as their own brother, sister's son or born to another family within the same village. Babies are born, then throughout childhood or into adulthood, experience past life memories. Information is revealed by the reincarnated child that could not have been known, then backed up by behaviors indicating some connection with the behaviors of the deceased.
Documented cases can be found on Iisis.net: The Institute for the Integration of Science, Intuition and Spirit. You'll read examples of research into cases where reincarnation has occurred within the same family, for example Lionel Ennuyer Reincarnating as His Sister's Daughter.
Our souls must therefore be travelling through time and space together, and our relationships as we experience them on the earthly plane must be dynamic and interchangeable. As a bizarre example, in one lifetime our mother may be our daughter and in the next, she's our mother again. As time is not relative on spiritual planes to our linear earthly time, our mother already deceased, may be waiting for us too to die and be reborn, then to bear children, so that she can become one of those children. The time for her to wait may be negligible.
It's also true that a spirit can choose to reincarnate as male or female. With all due respect this may be a reason behind some individuals being gay or lesbian. This author has a niece who is lesbian, her personal experience is feeling like a male trapped in a female's body. She believes her soul has bias toward male and that she was incarnated as the wrong sex. This however may have been of her own choosing before incarnation for the purpose of learning and experience.
According to The Law of One - The Ra Material, spirits who have reached a certain level of self awareness and progression can choose the time and location of their next incarnation, effectively choosing their parents. If unfavorable circumstances are chosen, for example poverty, then this is a learning experience in which the spirit enhances its universal understanding and likely empathy toward others in such circumstances.
Have you ever met someone for the first time and felt like you've known them for years? This is true for many couples or friends. It's possible that they have been travelling together through many lifetimes, for thousands of Earth years. The love that a couple has could literally endure for thousands of years, if not eternity. Two spirits' frequency of energy vibration, or energy center (chakra) balance, may be so harmonious that they're practically an extension of each other. Being with a different entity may not feel the same, not so harmonious or rewarding.
Likewise a mother who gives birth to, and meets her child for the first time, may feel overjoyed partly because of being reunited with an old friend. The new baby could have been, in a previous life, a sibling, friend, child or even parent.
Take from this only comfort. Cherish this life and know that the group with whom you travel in space and time are good companions, most likely for eternity. Others may come and go and you know who they may be. If your 'soul mate' has passed over, then you'll be reunited in circumstances of both your choosing. If a beloved family member or friend has passed, you may see them on the etheric plane when you go over, or sooner than you think if they choose to reincarnate nearby. Newer family members may exhibit behavior that reminds you of someone you remember well. So smile and know that you are always together with your companions, whether here, or as spirit guides, or on the other side - and that love is literally never ending.
Here's a good related book on Old Souls: The Scientific Evidence for Past Lives: Scientific Search for Proof of Past Lives.