From my research (I was considering buying some miles), the purchased points can be transferred to another member, but I think the transferred miles cannot be combined with other member's own earned miles. You may want to check with Eva Air if purchased miles are treated differently when transferred.

If you have Capital One or Citi TY points, you can transfer them into your account to make it to the 50% threshold for flight redemption as credit card points are treated as earned miles.