As a stepfather myself, I can only advise you to be yourself. The ages of the children is not stated. If necessary, explain to your future stepchildren, that you are not there to take over from their mother, or to take their father away from them. Talk to them about their mother. Ask them what was she like. Insist on seeing photographs of her. Comment on how beautiful she looked. Then explain that you love their father, who is very, very sad at the loss of their mother, and you wish to make him less sad and also to love them - not as a mother, but maybe as their big sister. As a big sister there will be times when you will have to tell them off, but you will only do that because you care and love them.A lot to do, but you don't have to do all at once. If in doubt, or in over your head, leave discipline to the Father.