If you are 'in the repair process', does that include a carpenter or someone else qualified to evaluate the structure? A professional opinion might be a good idea - at least it would help you sleep at night knowing you had a pro look at it.

Having said that, it looks pretty solid to me. Good advice from kudzu about poking it a bit.

Thank you kudzu9 for the
advice and thank you toxcrusadr.

The solid wood beam seems still solid, didn’t feel soft or
sponginess. We aren’t too sure about the
joist (particle board), like you said, it’s not very thick.

I had two construction companies came today to see if repairs
or replacements are needed and requested estimates.

One construction company recommended reinforce it by put in
three additional joists and two short beams to support the joists in a cross
direction.

The other foundation company told me that the damaged beam
and joists need to be replaced. He because
the moisture level is high and that level will not decrease over time. He explained that once the moisture get
inside the wood, it will not and can’t be dried. So the beam has lost its strength to support
the structure which would cause the floor (both 1st and 2nd
floor) to sag in less than a year. He
also said if I don’t replace them now, it will cause more damage to the house
and will cost me more to replace it then.
I feel like that guy was trying to scare me so I will hire them for the
job.

Your instincts are correct: the second contractor sounds like a scam artist. Most of what he told you is totally bogus. Stay away from him.

Since I can't examine it in person, I won't second guess the first contractor. However, if you haven't experienced sagging, I'm skeptical you will. I'd be interested to know what the first contractor is saying he would charge to do this.

The first contractor quoted me $2750 plus tax for the reinforcement.

That sounds rather steep. This is not a major fix.