In medieval Europe, names often (albeit not always) represented one of three things:
- Where you (or your family) were from
- Who you (or your family) were from
- What you (or your family) did
For instance, the Scotts and Irish used the Gaelic word Mac to create clan names such as MacDougall (literally: "son of Dougall") while the Scandinavians used the suffix -sen or -son; the French used the word de (and its cognates) to say where they came from, such as d'Orléans ("from Orleans") or Dupont ("from the bridge" -- not on its own highly descriptive); and all over you had names like Smith (any of a number of "smithy" trades such as blacksmith), Sawyer ("wood cutter"), and La Forge (literally "the forge", i.e. "blacksmith").
It's conceivable, then, that the letter 'y' in your names could be the demarcation between given and family name, where the family name could be any of these (and more): Myra could be from a house founded by someone named Ra; in the Old Tongue, maybe "tho" meant "carpenter", making Alytho something akin to Al[ice] Sawyer; Syng's family might come from the region known (or formerly known) as Ng. Sometimes names became more simplistic, literally meaning "son/daughter of [mom/dad]", so Theyna might be the daughter of Naytra, the son of Trayvis, the son of Visytra, etc. (In this form, you might conceivably have an Arabian-style "formal name"1 that strings all of that together: Theynaytrayvisytra.)
None of this implies a stringent structure to the parts of their names. For instance, Syng could have a brother named Jokitryng, and their friend down the street might be named Sytrovalliance. You could even conceivably have a clan/house that took the full name of the founder, such that Myra's name might more accurately be Myraytro.
Using the 'y' in this form doesn't necessarily require that it always be pronounced the same, either. For instance, at least in modern usage (and at least here stateside) the names McDonald and MacDonald have slightly different pronunciations, even though the former is technically just an abbreviated form of the latter. As far as constructing and pronouncing the names go, 'y' is just another letter and follows all the rules it otherwise would; there might have been a time when it strictly had a single sound, but the language has evolved, as languages do, in a way that makes these names easier to say and more natural to hear.
1 In ancient Arabia (possibly modern as well? not sure when or even if it fell out of fashion) a person introducing himself formally would for all intents and purposes lay out his entire geneology, stringing together the name of each father, father's father, father's father's father, etc. with the word ibn, meaning "son of", such that (for instance) I might introduce myself as:
Travis, son of Richard, son of Robert, son of Robert, son of Robert, son of Jacob, son of... [Yes, this is accurate, as far back as I can remember off the top of my head, though we actually know our genealogy as far back as the Normans, pre-invasion of England.]