Alright i could get it to work 2-3 x that suddenly both characters did attack the same target, but i cant reproduce it. Iam not sure what iam doing wrong. So far i noticed that when i target my main character first and press the assist macro sometimes my alt attacks too, but that happens not always. Hope some are around who did play ROM and can help me out here, will test more.

edit: something strange happens sometimes: i do the same like described above, but my alt targets and attacks a different mob opposite to me even i did only target the one i attack.