1. You have already asked this question earlier on the platform.
2. Please understand that a company is an artificial person. How can it sign? Therefore the company through its board of directors appoints some trusted person to act for and on behalf of the company.
3. The company does the above through a simple board resolution which is signed by the directors and seal of the company is stamped on such a resolution.
4. This is enough for the person named in the resolution to act for and on behalf of the company.
5. A separate power of attorney is not required from the company in the favour of such person.
6. If you are availing loan, then your lender bank will do the due diligence for clear title of builder.
7. Since you say that the project is approved by nationalised banks, then what is your apprehension?? I do not understand.
8. Also please bear in mind that the person authorised by a board resolution to do certain acts on behalf of the company cannot opt himself out from the acts which are done by him on the company's behalf so long as the board resolution authorising him stands. However if the company decides to revoke the authority of such a person, then it will pass necessary resolution in that behalf. Thus if Mr. Z were to do any acts without a valid board resolution authorising him to act for the company, then such acts are invalid.
9. You also have the letter on company's letter head stating that the company has authorised Mr. Z to do xyz.
10. Yes, for the other owners who are individuals, they can give a power of attorney to Z to act on their behalf.
11. I think in your case, the company must have authorised some trusted person to act on its behalf and this person alongwith the other owners who are natural persons, must have executed a power of attorney in favour of Z. If that is so then it is enough. Nothing further is required.
12. It is good to be diligent but not excessively.