In LDS theology “spirit” is refined matter.
D&C 130:7, 8: There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes; We cannot see it; but when our bodies are purified we shall see that it is all matter.
This is similar to Tertullian’s view of of what makes up “spirit” per Leo Donald Davis.
Leo Donald Davis states “Though a step forward in Trinitarian thought, it is clear that Tertullian’s view is still somewhat immersed in the sensible. Spirit is for him really only attenuated matter, and imagination so pervaded his thinking that he could explain the unity of the divine substance in terms of an organic continuity and of accord within the human monarchy. His view as father and Son as of one quasi-material substance is different from the consubstantiality (homoousian) that will form the basis of Nicaea’s pronouncements.” (Leo Donald Davis, SJ, The First Seven Ecumenical Councils, The Liturgical Press, pg 45)
I do not believe there exist any beings on Earth, in Heaven, or in Hell, or anywhere else that are not composed of some sort of matter, whether that matter be refined, attenuated, or something else. So to your challenge of how anything but an immaterial being can be with all the faithful in Heaven always, I just turn it around and ask how can an immaterial being be anywhere ever?