As others have said, Vhairi is nonsense.
Mairi is the Gaelic form of Mary. It's pronounced 'Marry'.
Mhairi is the vocative form of Mairi. Gaelic nouns change spelling depending upon their grammatical usage. Mhairi is the form used when speaking to someone with that name. In Gaelic, 'Mh' is pronounced 'v', and so the name sounds like 'Varry'. 'Vh' at the beginning of the name makes no sense at all. If it's used, it will just look totally illiterate. Sorry, but that's true.
It is occasional modern Gaelic usage to call girl children 'Mhairi' rather than 'Mairi', but never, ever, 'Vhairi'.
FWIW Hamish and Seamus are the same name - the Gaelic version of James. Seamus is the actual name; Hamish is an anglicised version of the vocative form, used when speaking to somone with that name. Also in (relatively) modern Gaelic usage, the two have become accepted separate forms of the name.
Eilish/Ailish are Gaelic forms of 'Alice', pronounced 'Ay-lish'.
How are you intending to pronounce Roisin? It's normally 'Rosheen'.
Blair is a Gaelic word meaning 'field' or 'flat grassland'. Why would anyone want to name a child that?
Also as others have said, Bryn is a Welsh male name meaning hill or mountain, and signifying massive size and strength. Also closely associated at the moment with large and well-built deep-voiced opear singer Bryn Terfel.
It puzzles me. Why do people think that the traditional languages of parts of the UK can have their spellings/meanings ignored?