Using my Sister

I'm Jason 34 oldest of 3 and single, I graduated university and done very well since with a good career and have my own home. My brother Michael 27 is in the Navy and overseas, my sister Marsha 30 divorced 2 children and her loser husband cleared out and left broke and as she was 8 months pregnant when he left unemployed. Our parents aren't able to help as they live in a retirement village and aren't financially well off. So that left me her nerdy brother and I took her and her child in and shortly after the other one arrived. I also got her divorce proceedings started and now she works as my live in housekeeper/lover. She has no skills to get a good enough job to fund her and her children's life. As I'm no ladies man I started to pay her to keep my house clean, do laundry and cook meals. I also pay any of her bills that crop up beyond her ability to pay. As I didn't date I use to masturbate, usually after the children were asleep in their beds and in my room. Then one night after a busy day, she had put the children to bed and came to ask me a favor. She usually just walks in and she did that night and caught cock in hand masturbating. She quickly left my room and I now deflated put my cock away and went to see what she wanted. I asked what was the problem as I'm was left alone in room before that night. She needed money to buy clothes and shoes for her children and some underwear for herself. I gave her my card and told to get what she wanted next morning. She knows me very well and knew I'm no ladies man and masturbating was my way of coping. So she straight out offered to finish me off, because she had ruined my previous attempt. This took me by surprise, but my cock started to harden up, so I agreed. We went to my bedroom and she had undress completely and lay on the bed and then she shocked me by completely undressing herself. She told me I would have the full experience, seeing alive naked woman. Of course I came rather quickly and she cleaned me and said she would do me again. I started to harden up again with her playing with my cock, but as quickly as before. So she decided to suck me me off and I harden up quicker, instead of masturbating me she mount me and rode until I came inside her. I was shocked that she would mount and fuck me and then asked what about you getting pregnant to me. She said it wasn't likely as she was still breast feeding the baby, then asked had I enjoyed it. I said I had really enjoyed it, she then asked how many woman I had fucked. I didn't want to said I had hired hookers when away and so said one, which she took to mean her. I had meant it to mean one other, but she seemed happy to have taken my virginity and so I left it at that. The next night she put older child to bed and was breast feeding the baby, I was making a coffee and asked if she want something too. She said she didn't and asked me would I like her to sleep with me again, Yes I said with any hesitation and she smile and said okay it's the least I can do for you. She has now weened the baby, but still sleeps with me every night. She says we make a good couple and if I don't mind she will stay with me. I said I don't mind and enjoy your company a great deal. I've also gotten a promotion and am selling my home to move to the new job in July. I've already purchased a new house there and we hope be moved by the 4th. It is also closer to our parents and Marsha says she will share my room still and if I want she will have a child for me. I would like to be father, but unsure if I should and that what I told Marsha. She said she won't take precautions and leave to chance.