Question: Should the ashes of my long deceased Grandfather be moved to be placed next to those of my recently deceased Grandmother in the same columbarium? What should be the considerations?
Answer: Before deciding, you should consider these points –
 If your Grandfather has passed away for many years already, without any signs of still being around as a restless spirit, who is not yet reborn, the whereabouts of his remains does not really matter if there was no request.
Moving his remains would then be with that of your Grandmother would be more of a matter of sentimental consolation and convenience for visiting family members? If so, whether to move the remains or not is arbitrary.
There should NOT be thinking, hoping or praying that he in person should stay here ‘with’ Grandmother, which suggests that they should be wandering spirits. They should both be guided to reach Pure Land, where there is only blissful progress to Buddhahood, without any suffering.
 Blessed Bright Sand Of Golden Light (金光明沙) should be scattered on the remains of both, to help facilitate good rebirths, if not yet reborn. For more on this sand, please see  at https://purelanders.com/2015/12/30/important-guidelines-2-during-dying-pure-land-passport-section-4b.
 What most important is to practise more of this procedure: purelanders.com/wake – at home, and/or near the remains, focusing on more sincere mindfulness of the name of Āmítuófó (阿弥陀佛) (i.e. Niànfó: 念佛).
 If deciding to move the remains, before moving them, as at purelanders.com/wake, the Guidance Text (开示文) adapted accordingly, followed by the Repentance Verse (忏悔偈), Niànfó and dedication of merits (回向) should be recited sincerely. Again, more time should be focused on Niànfó, with it done for at least 10-15 minutes before rehousing.
A reminder from https://purelanders.com/2015/12/30/important-guidelines-3-after-dying-pure-land-passport-section-4c: ‘If the deceased did not like sea burial, and preferred the urn to be kept in a certain place, for peace of mind, it should be kept there (e.g. in a temple’s columbarium or at home). However, upon storing the urn, there should be reminder to the deceased, who might still be around, to not be attached to the urn or its location. As there will be rebirth eventually and possibly suddenly due to the law of karma, he or she should continue to Niànfó sincerely, to be reborn in Pure Land swiftly.’