Will we recognize people we knew on Earth? Of course. Our individual personalities will not cease to exist, nor will our memories. If they did, eternal salvation (or God forbid, eternal damnation) would have no meaning. Therefore, though until Christ’s return we will leave our bodies behind, our individuality is still imprinted on our souls. Through he power of the Beatific Vision, our eyes will be opened to perceive God’s creation as it was meant to be. Ergo, we will be able to ‘look’ upon each soul and recognize them.
We can also be confident that relationships will not ‘disintegrate’. When Christ raised from the dead, both His divine nature and His human nature knew the Apostles, and they knew Him. Christ also speaks about the final judgment, when those who did His will will enter into eternal life. They are depicted as saying “when did we feed you…clothe you…visit you…”. Notice that they say this as a group. It stands to reason that there is a knowledge or relationship with each other after death.
You say that it doesn’t seem right that marriage will be “totally torn apart and obsolete”. Your first part is correct. When Christ says that in heaven people are neither “married nor given in marriage”, He does not mean that Marriage is destroyed (remember, “what God hath joined together, let no one put asunder”). But marriages will most definitely be “obsolete” because they are built on imperfect, human love. The relationships we have with our spouses in Heaven will be so far beyond human comprehension, the love will be so perfect, that the term “marriage” will indeed be obsolete. Additionally, one has to look at the primary purpose for marriage, namely, to provide a permanent, safe environment for procreation. God created marriage for the purpose of uniting man and woman (“the two become one flesh”). The two-fold meaning of this being that they become one flesh both in the marital embrace, as well as more literally in the consequence of that embrace, i.e., children.
In heaven there will be no need for procreation, as procreation only occurs on Earth (no new human souls are created in Heaven). In addition, the unitive power of the conjugal act will also be rendered obsolete by the new love between husband and wife, made perfect in the presence of Almighty God. How lucky will we be that marriage will pass away! And even more good news: that perfect love, freed from the necessity of the unitive conjugal act, will be the constant state of being between every relationship we have in heaven! So much as we love our spouses on earth, indeed, even moreso, we will love and be loved in every relationship, family and friends!
Finally, you asked how knowledge that a loved one did not make it to heaven will affect us. A beautiful explanation of this was given by St. Thomas Aquinas. He said that the suffering of the damned in Hell will actually add to the elation of the elect in Heaven. He realized that, by virtue of the Beatific Vision, we will have full knowledge of everything a person in Hell did to end up there. Therefore, in seeing God’s divine justice at work, we will understand His perfect love even more.
Ultimately, we know that Heaven is a place of perfect, eternal happiness. We may not (indeed, cannot) understand what it would be like to exist in such a state of bliss, but we should trust in the Lord’s promise regardless.
