you have not mnetioned if your step mom is alive or not.if your step mom is alive then from the total assests her share will be 1/8th and from the rest of the assetts(7/8) , each brother shall have 2/9th and each of you sisters shall have 1/9th.

and in case if your step mom is not alive then share of each brother and sister shall be the same as mentioned before but now it shall be out the whole assets without deducting the 1/8th share of the woidow (step Mom). if you require more information or details you can call during office hours ,working days.