Your sister cannot stop you seeing your mum, in fact she could get into a lot of trouble in stopping you.She cannot deny your mum contact with her daughter..I know this because I have 3 sisters(I live with mum).at first i thought your post was one of my sis! The s.w. is arranging for my sis to see our mum(I have not stopped them,they have refused mediation and were all squabbling before I got involved) My advise to you is first get in touch with the s.w., I would ask for mediation to get the issues resolved. If your sister refuses mediation, then the s.w will ask your mum(without your sister present) if she wishes to see you, of course your mum will, then the s.w. will arrange for you to see your mum..Try not to involve the police as it will only make a fragile situation worse.It is actually against the law for your sister to deny your mum contact with you,her daughter..I was told this by a solicitor(you can get free legal advice at the C.Centre and A Z)and a judge will remove your sister and she could be jailed, she is not in a position to deny you access, weather she lives with your mum or not..So get in touch with the S.W. first,..It is awful when there is unescerrary conflict and petty arguments, this is such an important time for everyone, if you can, try and smooth it over with your sister, offer to help, as it really is better to be civil and communicating than estranged...But you do have rights..Let us know how you get on, take care x