If you're looking for rent estimates for MTR, there is a great tool called Pricelabs.

Our property management company wants to sell 3 apartment blocks for us approximate value 2m maybe slightly more, can we ask them to accept 4% sales commission?

It’s a good move to have a contractor walk through before making an offer to estimate costs and timeline. 

I'm getting a contractor/ structural engineer to come by and help me draw estimates and understand how serious these issues are.

If yes then what should his/her credentials should be and "approximate" cost?

Yes I think estimating 5% would be a good start and then once you know the school district you can get a better idea of what to expect.

If you can get a loan at the 6.5%, you're saving another 5k a year off your estimates. 

It’s always a good idea to consult a local real estate attorney and title company for more accurate estimates in your area.

During your initial walkthrough, inspect the property for any major issues such as structural damage, roofing problems, plumbing, and electrical concerns, while documenting all cosmetic and functional issues with detailed photos and notes.Once you confirm the property’s potential, finalize your ARV and calculate the repair costs using either a reliable estimator or insights from contractors.

In 8 years and over 20k reservations we have had 15-20 incidents I would estimate.