=# create role a login;
CREATE ROLE
=# create role b login;
CREATE ROLE
d=# create schema a;
CREATE SCHEMA
=# create table a.t1(id int primary key);
CREATE TABLE
=# create table a.t2(id int references a.t1(id));
CREATE TABLE
=# alter table a.t1 owner to a;
ALTER TABLE
=# alter table a.t2 owner to a;
ALTER TABLE
=# alter schema a owner to b;
ALTER SCHEMA
=# grant all on a.t1 to b;
GRANT
=# grant all on a.t2 to b;
GRANT
=# insert into a.t1 values(1);
INSERT 0 1

d=# \c - b
You are now connected to database "d" as user "b".
d=> \dt a.*
       List of relations
 Schema | Name | Type  | Owner 
--------+------+-------+-------
 a      | t1   | table | a
 a      | t2   | table | a
(2 rows)

d=> \dn+ a
                List of schemas
 Name | Owner | Access privileges | Description 
------+-------+-------------------+-------------
 a    | b     |                   | 
(1 row)

d=> insert into a.t2 values(1);
ERROR:  permission denied for schema a
LINE 1: SELECT 1 FROM ONLY "a"."t1" x WHERE "id" OPERATOR(pg_catalog...
                           ^
QUERY:  SELECT 1 FROM ONLY "a"."t1" x WHERE "id" OPERATOR(pg_catalog.=) $1 FOR KEY SHARE OF x

d=> \c - postgres 
You are now connected to database "d" as user "postgres".
d=# insert into a.t2 values(1);
ERROR:  permission denied for schema a
LINE 1: SELECT 1 FROM ONLY "a"."t1" x WHERE "id" OPERATOR(pg_catalog...
                           ^
QUERY:  SELECT 1 FROM ONLY "a"."t1" x WHERE "id" OPERATOR(pg_catalog.=) $1 FOR KEY SHARE OF x

GRANT USAGE ON SCHEMA markup TO markup;