you won't get a definitave answer without a structural ( residential) engineer actually looking at the situation on site. tey'll have to do a load calculation of whats above and know what the foundation and footing and soil conditions are like below.
edit* I'm probably missing other factors as well, but you get the idea.
You need to get an engneer in there to be on site and spec what size beam and what material to use.
This is not a "I think this is strong enough" type of deal.
Bad things can happen real fast is done wrong.
No amount of pictures over the net from any place will get you any more then guesses.
you should take the advice given above an hire a professional engineer that specializes in residential construction. They will determine the size and type of beam you need, and the installation requirements.
Better to spend a little money to determine what you need to do than to end up with structural issues which will cost a lot more money to correct.
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