The plural form of the noun engineer is engineers.
The plural possessive form is engineers'.
Example: All of the engineers' submissions will be evaluated on an equal basis.
engineers'
The plural form for the singular noun engineer is engineers.
The plural possessive of "technicians" is "technicians'": The technicians' expensive equipment was locked up at night.
The plural form of the noun inventor is inventors.The plural possessive form is inventors'.Example: All of the inventors' chances for receiving the grant are equal.
The plural form of the noun inventor is inventors.The plural possessive form is inventors'.Example: All of the inventors' chances for receiving the grant are equal.