allOf with same property names

Yes this is allowed. allOf does not actually mean "merge" (even though some tools handle it as "merge"). It means that an instance is considered valid if it matches each of the listed subschemas independently.

Consider this schema:

type: object
required: [id]
allOf:
  - properties:
      id:
        type: integer
  - properties:
      id:
        minimum: 0

 {"id": 5} is a valid - because the "id" value (5) matches both "type: integer" and "minimum: 0".

But {"id": -8} is invalid - because it does not match the "mininum: 0" constraint defined in the second subschema.

Because the subschemas in allOf know nothing about each other, it's also possible to create "impossible" schemas with contradicting constraints. For example, this schema does not match anything because "id" cannot be both an integer and a string:

type: object
required: [id]
allOf:
  - properties:
      id:
        type: integer
  - properties:
      id:
        type: string

Hope this answers your question!