I can understand your situation. It’s hard to teach new language using English if the students have a low level of English.
You say you shouldn’t be speaking Arabic at all. I think some schools apply this rule to avoid a situation where teachers use only the native language to teach. I think the use of limited Arabic is acceptable. For example, the translation of individual words that are difficult to mime could be acceptable; also explaining an exercise in Arabic could be quicker than explaining it in English. The students can then spend more time doing the exercise rather than trying to understand what they should do. However, I don’t think you should use only Arabic. Maybe the first thing to do is to find out if some Arabic is acceptable in class.
I think it’s very useful if students understand instructions in English. You could spend some time teaching the language of frequently used instructions, e.g. work in pairs, listen and write down the answers, be quiet, look at the board, turn to page 29……..
Can you draw pictures to illustrate these activities? Or do you know somebody who can? You can have students match instructions with pictures of people carrying out the instructions. You can follow up with mime and students say what you are doing. You can also give students the instructions jumbled up and they put the phrases back in the right order. I think this is a priority with the class because you will be able to do more work in English.
You say you use miming with the class. This is a very good way to teach new vocabulary. Here are some other things you could think about:
Use the opposite; e.g. full and empty
Use realia (the real object; e.g. tissues, videos, bags to teach this language)
Explanation; use a simple definition in English. Teach students language such as “this is something you use to open a door”.
Translation; to be used carefully
Short stories; e.g. to teach the word “disappointed”. John was very excited about going to the cinema. At the last minute, his mother told him it wasn’t possible. John was very disappointed.
I hope this will help. Please write in again if you would like more ideas.