1)
Ele o fez para mim.
<He "it" made for me>
He made it for me.
Tip: Avoid this kind of construction, they are what we call "mesóclise" - no longer used. We prefer simpler forms, even in written communication.
2)
Ele o fez para eu dar-lhes de aniversário.
<He "it" made for I give-them "of" birthday>
He made it for me to give them for their birthday.
In the most simple way you would say:
Ele fez para eu dar à eles de aniversário. <He made for I give to them of birthday>
When refering to a mean or reason, you may use:
1) Pelo / pelos ("by the")
Merece um prêmio pelos seus esforços - You deserve a prize for your efforts.
2) Por causa ("by cause"), porque ("because")
Precisa ficar, por causa da doença - You must stay, because of your illness.
Por causa requires a noun. (a doença)
Precisa ficar, porque está doente - You must stay, because you're ill.
Precisa requires a verb. (estar doente)