Interesting. For me (west coast US), "peg leg" rhymes, both with the short "e" sound. "Leg" with the long "a" sound doesn't sound wrong necessarily, but I wouldn't say it. But actually I think sometimes my pronunciation moves to somewhere in the middle between rhyming with "beg" and rhyming with "plague".
As for
Megan, I would normally think to pronounce it "Meg-an" with the short "e", though I have heard people say "May-gan" which doesn't seem wrong, and now that I think about it, my pronunciation might fall somewhere in the middle of these two as well.
As for
Tegan, I've always heard it pronounced TEE-gan.
and this is but an island in an ocean