宿泊者以外はお部屋にあがれませんって英語でなんて言うの？

Do not enter the room unless you have a reservation. - This is saying that if you have not booked and payed for a room in the hotel then you cannot enter the rooms.
It is common for guests to bring a friend to the hotel room so this needs to be made known at check-in if that is the policy.
Rooms are for paying guests only. - This also means that if you have not payed for the room then you cannot use the rooms.

"Guests only in hotel rooms" is a clear way of saying that no one other than guests are allowed in hotel rooms.
"Please can guests refrain from taking non guests to the hotel rooms" is a polite way to ask guests not to take non-guests to their rooms.
"Residents only in hotel rooms" is very clear that only people staying in the hotel are allowed in the rooms.

A guest is a paying customer who is paying to stay at the hotel. They may have friends or family who want to come in to use the facilities which is not in the best interests of the hotel. You could say: I am sorry but we only allow guests entry to the hotel rooms, it is hotel policy.

Here are three ways that you can express this idea to incoming guests into the hotel. Notice that we can refer to people who are not staying at the hotel as, "visitors," or, "outsiders." In addition, we can also say that, "only guests," are allowed to have the same effect as the other two examples.

"We kindly ask that only hotel guests occupy the rooms." This a polite way of asking that only people staying at the hotel, go into (their) rooms. "Occupy" means to use something. "This room is occupied". Or, if you work at the reception at the hotel & someone walks in asking for a room but you don't have any, you could say "I'm sorry. Unfortunately, all the rooms are occupied this evening."

"Only hotel guests are allowed in the rooms." This statement is a bit more direct & is more of an order saying that only guests can be in the rooms.

You can probably guess that my three sentences went from direct, not rude, but direct, to more polite and calm. So, depending on the situation you can judge which one you need to use. But, to be safe, the third is the kindest way of saying it.

Try one out, see how it goes, and see which one suits you.

I hope this helps.
Have a great day.
Will

The best way to describe the difference between someone that is staying at a hotel and someone that is not is talk about if they are a 'guest.'

Someone staying at a hotel is referred to as a 'guest'
And someone that is not staying at the hotel is a 'non-guest' or not a guest.

EX)
Only guests can enter the room.
Non-guests are not allowed in rooms.

When you want to explain to a person that only hotel guest are allowed into the rooms and not anyone not staying at the hotel; you may explain this in the following ways:
-The only people that may be allowed into the rooms are hotel guests.
-We only allow guests into the rooms. Unfortunately, non-guests may not enter the rooms.
-Only hotel guests are allowed into the rooms. You may not enter the rooms unless you're staying with us.

If you would like to tell someone that only hotel guests can enter the the rooms, you can say something like "Only hotel guests can enter the hotel rooms.Thank you for your cooperation and sorry for the inconvenienced caused.". This is a polite way to express this to someone.

宿泊者はGuestと言います。又は、ホテルのお客様もGuestです。
訪問者はVisitorと言います。

Can~ = 何かのことができる。（Can enter = 入ることができます。・入れます）

1) Only guests can go up to the rooms.
(宿泊者のみ部屋に上がれます。)

2) Only guests can enter the hotel rooms.
(宿泊者のみお部屋に入れます。)

3) Visitors are not allowed in the hotel rooms.
(訪問者はお部屋に入れません。)

1. It is our policy that visitors of hotel guests are not allowed inside
   the hotel rooms.
   A policy is a rule that cannot be broken unless prior permission has been
   granted.
   Visitors of hotel guests are those people who have not paid for
   accommodation at the hotel but are simply visiting friends or family
   who have indeed paid for their hotel stay.

2. Only paying guests are allowed inside our hotel rooms.
   Paying guests are those people who have made reservations at the hotel
   and have paid for their accommodation.

The above mentioned statements are all clear on the hotel's request that that the visitors stay out of the rooms. The first two sentences are used when a guest of the hotel directly asks you if they may bring a visitor to their room for the day. They may ask, "can my friend go up to my room with me?", and then the appropriate response would be either sentence one on sentence two.

The last sentence response (No visitors are allowed, only guests) will work best if the hotel will make a sign of the no-visitor policy.

1.部屋へのアクセスはお客様に限ります。
2.部外者がホテルのルームに入ることが禁止です。

"limited"は「限定」、「限る」という意味です。この場合は"restricted"も使えます。

"outsider"は「部外者」という意味です。「よそ者」や試合などで勝ち目のないチームや選手（特に馬に使います）という意味もあります。

1) “Only checked-in guests are allowed in the rooms.”
（チェックインされたゲストのみ、お部屋に入室できます。）
「宿泊者」は、checked-in guestsの他、registered guests（登録済みのゲスト）やホテルの場合、hotel guests （ホテルのゲスト）などと表現できます。

2) “Visitors are not permitted to enter the (hotel) guest rooms.”
（訪問者の(ホテルの)お部屋への入室は禁止されています。）
not permittedは、禁止されているという意味で、ややフォーマルな言い方です。

代案を提示する際には、以下のようなフレーズを使うことができます。
“You are welcome to meet with your visitors in the lobby / lounge.”
（ご来客の面会には、ぜひロビー・ラウンジをご利用ください。）

1) Only guests are allowed in the rooms.
客室に入れるのは宿泊者だけです、という意味です。
Allowは許可する、許されるという意味ですね。

2) Visitors are not allowed in the rooms.
この文も似たような意味ですけど、ビジター（宿泊者以外の人）は客室に入れ
ないということなので、ニュアンスが若干変わります。

You could use any of the above sentences to explain to someone that only hotel guests are allowed to enter or use the rooms and facilities and anything else is strictly forbidden or against hotel rules.

• Only hotel guests are allowed; meaning that only people who are booked into the hotel are allowed to use rooms.