Dear cherryrose,
can totally understand what you are going through. What is your nationality? Ok here is what you should do.
to apply for your mum's and sister's visa you should have the following.

Your passport copy
Your residence permit copy
your birth certificate
your sisters birther certifcate and passport copy
your mums passport copy.
Your husbands passport and residence copy - Just in case

Go to the immigration near the Airport. Complete the forms (there is a bit of arabis woriding , hence you would need help from someone to fill it up) then go meet the captain (he is seated in a seperate room inside) to obtain his approval. Once he approves it (believe me there is NO reason for them to reject it) you can make the necessary payment. QAR 55.00 per visa Valid for 14 days. they will issue a receipt which you would need to give at least 24 hours for the visa to be processed. you can check online to see whether it is approved. (www.moi.gov.qa)

The visa will be valid for 14 days which can be extendable for another 14 days. total of 28 days. If you wish to extend for another 28 days (total of 56) you would need to visist the Qatar Airways Head office loacted at the Airport Road and ask for te visa section. Then you would need to pay a fee of QAR 350.00 per visa to issue a ticket to Bahrain. now this ticket that they issue is not valid for travel. It's an agreement between the immigration and Qatar Airways. and then you would need to visit the immigration for the extension.

Now this is for the 28/56 day tourist visa. Are you looking for the 3 month visa? Let me know if you need any other info.
tc

ps: sorry for the long mail! :)