Praise be to Allah.
It should be noted, first of all, that whoever is one of the people of Paradise will be in eternal bliss, and will not grieve, or feel exhausted, or feel distressed, or worry; he will be distracted from everything else apart from the state of eternal bliss and everlasting joy in which he finds himself. Nothing will ever spoil or tarnish his delight. Allah says (interpretation of the meaning):
“Verily, the dwellers of the Paradise, that Day, will be busy with joyful things.
56. They and their wives will be in pleasant shade, reclining on thrones.
57. They will have therein fruits (of all kinds) and all that they ask for.
58. (It will be said to them): Salaam (peace be on you) — a Word from the Lord (Allaah), Most Merciful”
Those who are in Hell will not harm him, no matter who they are. Allah has told us about the split, division and enmity that will occur between close friends and loved ones on the Day of Resurrection, except those who were pious and feared Allah. Allah says (interpretation of the meaning):
“Friends on that Day will be foes one to another except Al‑Muttaqoon (the pious)”
Al-Bukhaari (3350) narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “Ibraaheem will meet his father Aazar on the Day of Resurrection and there will be darkness and dust on Aazar’s face. Ibraaheem will say to him: ‘Did I not tell you not to disobey me?’ His father will say: ‘Today I will not disobey you.’ Ibraaheem will say: ‘O Lord, You promised not to disgrace me on the Day of Resurrection; what will be more disgraceful to me than curing and dishonouring my father?’ Allah will say: ‘I have forbidden Paradise to the disbelievers.’ Then it will be said: ‘O Ibraaheem, what is beneath your feet?’ He will look and will see a hyena stained with blood, which will be taken by the legs and thrown into Hell.”
It was also narrated by Ibn al-Mundhir, who added: “When he sees him like that he will disavow him and will say: ‘You are not my father.”
Fath al-Baari, 8/500
Thus it is clear that the connection will be severed between the people of Paradise and the people of Hell who are their relatives but are disbelievers and will abide for ever therein, even if they were the closest of people to them, and they will no longer feel an attachment to them and no longing for them will spoil their joy.
But if two people are both among the people of Hell, it will not benefit them to meet there or to see one another, as each of them will be punished because of his deeds and distracted by the state of pain and torment in which he finds himself. It will not benefit him to see his family members with him or all the people of Earth:
“It will profit you not this Day (O you who turn away from Allaah’s remembrance and His worship) as you did wrong, (and) that you will be sharers (you and your Qareen) in the punishment”
Rather, if those whom he loved and was close to were with him, he would wish that they would be sacrificed for him so that he could escape from this torment:
“The Mujrim, (criminal, sinner, disbeliever) would desire to ransom himself from the punishment of that Day by his children.
12. And his wife and his brother,
13. And his kindred who sheltered him,
14. And all that are in the earth, so that it might save him”
But if both are people of Paradise, but are of different degrees, then some of the scholars spoke of the people of Paradise visiting one another. In Haadi al-Arwaah ila Bilaad al-Afraah, Ibn al-Qayyim wrote an entire chapter on that, in which he mentioned a number of hadeeths and reports, the isnaads of which are not free of weakness; such reports cannot be taken as evidence. Some of that was also mentioned by al-Haafiz al-Mundhiri in his book al-Targheeb wa’l-Tarheeb, in a chapter entitled “their visits to one another and their mounts”. Despite the weakness in the isnaads of this chapter, the idea that the people of Paradise will visit one another and know one another there is obvious, especially as that will be part of their complete delight and joy there. This has been clearly stated by more than one of the salaf.
And Allah knows best.