I dont fully understand what you need.
You need to write a file like this ?
KNA1
KNVV
KNVV
KNVP
ADRC
ADRC
ADRC
ADR6
ADR6
AUSP
AUSP
KNA1
KNVV
.....
1- Make a select from KNA1 to gt_KNA1
2- Then make each select to the next tables using FOR ALL ENTRIES gt_KNA1 (so you will have gt_KNVV, gt_ADRC, etc)
3- You now have all the data, the next thing make a LOOP AT gt_KNA1, inside make a LOOP for each table u need, appending all to a gt_FILE with only a field of 1024 chars.
Something like this:
LOOP AT gt_KNA1.
"Concatenate all the fields you need
CONCATENATE gt_KNA1-field1 gt_KNA1-field2 ... INTO gs_file-line SEPARATED BY cl_abap_char_utilities=>horizontal_tab
APPEND gs_file to gt_file
LOOP AT gt_KNVV WHERE KUNNR = gt_KNA1-KUNNR.
CONCATENATE gt_KNVV1-field1 gt_KNVV-field2 ... INTO gs_file-line SEPARATED BY cl_abap_char_utilities=>horizontal_tab
APPEND gs_file to gt_file
ENDLOOP.
"for ech table like the one before
ENDLOOP.
"Here you will have gt_file with all your file needed
You should also add a id field at the beginning of the line so you know what entry correspond to with table.
Regards