* ORACEL SQL parser can not parse this dynamic SQL properly

  Execute immediate 'select * from table1 where column1 in :b1' using p1;

You could construct the SQL by concatenating the IN list dynamically,
but then you would not be using bind variable. The answer seems to be
dropping the dynamic SQL all together. In stead, convert the IN list
to an array with a function, such as this one by Tom Kyte:

create or replace function str2tbl (
str_in in varchar2
) return typ_tab_v2100 as
str long := str_in || ',';
i pls_integer;
tab typ_tab_v2100 := typ_tab_v2100();
begin
loop
i := instr(str,',');
exit when nvl(i,0) = 0;
tab.extend;
tab(tab.count) := trim(substr(str,1,i-1));
str := substr(str,i+1);
end loop;
return tab;
end;
/ 

and then use the TABLE function to get what you need. For example:

SQL> select * from tyu;

C1 C2          C3         C4
-- --- ---------- ----------
G  XX           1         20
O  XX           1         20
Q  XX           1         20
a  XX           2         10
b  XX           2         10
c  XX           2         10
d  ZZ           1         40
e  ZZ           1         40
f  ZZ           1         40
g  YY           2         40
h  YY           2         30

C1 C2          C3         C4
-- --- ---------- ----------
p               4          4
w               5          5

13 rows selected.

SQL> declare
  2  x varchar2(100);
  3  begin
  4  x:='1,2';
  5  delete from tyu where c3 in (select t.column_value from
table(cast(str2tbl(x) as typ_tab_v2100)
) t);
  6  end;
  7  /

PL/SQL procedure successfully completed.

SQL> select * from tyu;

C1 C2          C3         C4
-- --- ---------- ----------
p               4          4
w               5          5

SQL> rollback;

Rollback complete.

SQL> declare
  2  x varchar2(100);
  3  begin
  4  x:='XX,YY';
  5  delete from tyu where c2 in (select t.column_value from
table(cast(str2tbl(x) as typ_tab_v2100)
) t);
  6  end;
  7  /

PL/SQL procedure successfully completed.

SQL> select * from tyu;

C1 C2          C3         C4
-- --- ---------- ----------
d  ZZ           1         40
e  ZZ           1         40
f  ZZ           1         40
p               4          4
w               5          5

SQL> rollback;

Rollback complete.

SQL>