Spanish to English Bus/Financial Business/Commerce (general)

I'm sure this is a simple matter but it's got me doubting myself...

The context is this A deed of incorporation stes the following in a section on who own the 3,000 shares in a company. There are two partners, we'll call them A and B.

"A es dueño de trescientas participaciones sociales, números 1 al 300 (...) Le pertenecen por compra a B formalizada en escritura autorizada por el Notario X"
"B es dueño de dos mil setecientas participaciones sociales, números 301 al 3.000 (...). Las participaciones números 301 al 900, ambos inclusive, le pertenecen por compra a A formalizada en escritura autorizada por el Notario X" It hen goes on to say where the other shares (901-3000) came from, not pertinent to this question.

(For what it's worth, it's very possible that B is A's father by the way)

It seems to me clear that in the first case A bought his shares from B and in the second case B bought them from A as it clearly states the total number of shares that each holds and the share numbers thereof. My (Spanish wife however thinks that "por compra a" means "were purchased BY" as opposed to "were purchased FROM"

Hope this makes sense. It's got me in a proper state.