Dinneen’s dictionary has the singular as réalt and the plural as either réalta, réilteanna, or realtanna, so my guess would be that that represents a Munster form.
Interestingly, among the Aran Islands (in Connacht), the dialect of the southernmost island is closer to Munster Gaelic than to Connacht. http://www.aranislands.ie/2016/01/14/mapping-aran-irish-a-25-year-job/
So is "na suile" here talking about a specific pair of eyes, or eyes in general?
Does "the eyes" in the English sentence talk about a specific pair of eyes, or eyes in general? Without context, it could have either meaning, but it's more likely to be talking about a specific pair of eyes.
The same would be true for na súile in the Irish sentence.
Mar and cosúil le don't quite mean the same thing, but yes, in this sentence, you could probably use either phrase.
surely the word 'réaltaí' is a complete fabrication - réalt (singular) and réalta (plural)??? no?
In Munster Irish, the singular is usually réalt, and the plural réalta.
(With the caveat that there aren't hard borders between the dialects, and there are variations within particular regions - this speaker doesn't usually favour Munster pronunciations. She might have just misread the script).