. . . the beginning of the morontia span. . . .
One’s life on one’s natal world is the womb, so to speak, of the soul. The soul is morontial, but it is embryonic.
66:4.9 During the mortal life in the flesh the soul is of embryonic estate; it is born (resurrected) in the morontia life and experiences growth through the successive morontia worlds.
Sounds like we are going to be born again (resurrected), where we will be bonafide morontians.
Are Urantian Midwayers considered morontia beings?
I couldn’t find anything about your question, but I found this snippet: 38:9.9
I did find that cherubim and sanobim are near the morontia level.
Cherubim and sanobim are by nature very near the morontia level of existence, and they prove to be most efficient in the borderland work of the physical, morontial, and spiritual domains. These children of the local universe Mother Spirit are characterized by “fourth creatures” much as are the Havona Servitals and the conciliating commissions. Every fourth cherubim and every fourth sanobim are quasi-material, very definitely resembling the morontia level of existence.
(38:7.7) These angelic fourth creatures are of great assistance to the seraphim in the more literal phases of their universe and planetary activities. Such morontia cherubim also perform many indispensable borderline tasks on the morontia training worlds and are assigned to the service of the Morontia Companions in large numbers. They are to the morontia spheres about what the midway creatures are to the evolutionary planets. On the inhabited worlds these morontia cherubim frequently work in liaison with the midway creatures. Cherubim and midway creatures are distinctly separate orders of beings; they have dissimilar origins, but they disclose great similarity in nature and function.
48:5.1 In the worlds of mortal existence the seraphim is ably assisted by cherubim and sanobim; but when her mortal ward is delivered from the bonds of the flesh and starts out on the ascendant career, when the postmaterial or morontia life begins, the attending seraphim has no further need of the ministrations of her former lieutenants, the cherubim and sanobim.
Looks to me as though morontia life begins upon resurrection, even though one’s immortal soul began to exist here, as a soul embryo.