Four year engagement and outside children

Where do I begin? Long story short... I been in a relationship for four years. During, I got engaged and had my first child, a son whose one. I love my fiance to death, but I think I'm more embarrassed than anything. My fiance has three other children by two different women. Both women are terrible and I wouldn't know where to begin to describe them as an individual nor a parent. The oldest is 10 and my fiance Mother is raising him because his Mother is too busy running around and my fiance and I stay states away. The other two children are ages three and five and their Mother left the youngest outside my fiance Mother house when he was a infant because she didn't want to raise him. She does have him back now, but she abandoned him. Anyway I have not experience the life of the blended family and I want to do this before i get married to see if I like it and I feel the children need to experience it also. I suggested this to my fiance but now I think I don't want this because it's messy for one and its taken years to get to this point. I feel it's too late and I've wasted my time. This may not seem such a big deal, but it certainly is. His mother practically runs the show and it has gotten to a point where I feel she blames me. Why i don't know, but i think it's because I'm a damn good parent to my son and she feels I should do the same by the others, but i refuse because these women are worthless and one threaten me over Facebook. It's just too much and I blame myself for still being with him after he had lied to me. When we first met, he told me he had one kid, the 10 year old. I was like cool, I can work with that, what's one kid? Months later after he proposed and me falling for him, I learned from his friend, he had two other children. I was very upset because I feel if you lie about your kids, you'll lie about anything. He also lied to my parents too, he told them only one. So this is embarrassing to me because I told close friends besides my family about this great guy. Not that I'm worried about what others think, it's just embarrassing because how do I explain all these kids when it should be two? Oh yeah it from one kid, to three kids, to two kids, back to three kids! Yeah i know, confusing huh? Supposedly the oldest of the two, the girl don't suppose to be his, but like I said his Mother get the kids every weekend and there has not been a paternity test. Everytime there suppose to be testing done, it's never done. Confusing for any individual and it has made me not love him like before. His mother hates me like I'm the bad person. She never calls and check up on her grandson, hell she never even said congrats, in fact, she acts like he don't even exists. Did I mention, she has not met him yet? I sent her pictures of him and she never said anything, but she treats his others like a grandparent suppose to. She also wants him to come spend time with his other children, but only at her domain, which is states away. She won't even meet my fiance halfway with his children so they can spend time with us. It's just out of hand and the situation has exhausted me. My question is, am I wrong for feeling this way? Think I want to move on because I see a long messy road!