I like Tamsin. Tamsyn is horribly misspelled. Also, Bronte is pronounced BRON-tay, as anyone who's taken eighth grade English will know. If they want to name their daughter Bron-TEE (which I wouldn't recommend) they should spell it phonetically.
ETA: I was still wondering about Bronte, so I checked Forvo and asked my mother (she's British and an English professor). She says BRON-tay is correct, but I heard both pronunciations on Forvo. Now I'm intrigued! I would say, though, that I'm probably not the only one who's going to struggle with the pronunciation -- and even aside from that, I wouldn't suggest using Bronte. It has more than an air of pretension about it.
I've not only taken eighth-grade English, but also have an honours degree in English and have visited Haworth Parsonage in Yorkshire. I have never heard Bronte pronounced anything but BRON-tee in either the UK or Australia. Clearly, the OP is going to have problems in the US if this is the pronunciation she prefers, but it is certainly not incorrect.
I don't think Bronte, pronounced BRON-tee, sounds pretentious at all. It's reasonably common in Australia, at least, and I don't think anybody particularly associates it with the authors anymore.