Proper translation for "active table"?
I think this is a good example of terrible sentences craft in mandarin, translate to English, later attempt to translate the terrible sentences back to mandarin. 

It has nothing to do with taken seat or seat served, but serving.  

It is pretty clear to say this in English : 

Each waiters/waitress served : 4 tables max
服务生能接待的数目 ：最多4桌/台客人

Each waiters/waitress should only served 4 tables
服务生最多只能接待四桌/台客人


Just be careful when you read some "weird" mandarin and strange English translation. It is quite common as some restaurant owner refuse to consult people(not even amateur) to proofread their menu.