Contacted hours, over one week under the next

ezzmo

Hi I work as a disability support worker for an individual who has recently had a new team formed to support him at home 24/7 however his mum has requested she stays every second weekend and a day during the week, this has reduced the hours by 72 a month and 4 sleepovers, as a result staff are now down in available hours and having to do say 15 one week and 45 the next. Should be be paid 30 each week and the week we do more have that as overtime? 
Mum has now said she wants to be doing more hours which will again impact on us. 
My contract states 30 hours per week and sleepovers and then we claim extra for meetings, he is also funded extra for 2 to 1 shifts but our employers are telling  us we can come in to do 2 to 1 shifts to make up our hours which technically are over and above our contacted hours, the job advertised was for 9am to 9am following day, so staff doing 24 hour shifts. 

Any help welcome