Ok, I am going to go out on a limb here and divulge what I already know about the subject, personal experiences, and possibly some hope for you. Without picking up on your current energy, I could already perceive what you may be going through. Already I see a situation unfold in which you have had encounters with this individual who is now part of the family in some respects and, therefore, part of your energy network (what I like to call the connection you feel through your personal trust categories - mainly your family and those close to you). In sense, you are probably close to the family member the "sociopath" had a baby with and, therefore, by association, picking up on the sociopath's energy patterns, which are on a big scale, undesirable. This is something you cannot shake or you would lose the connection with the family member so you have to deal with it the best way you can. That's basically psychology and empath stuff combined. The real catch I see, however, is the secondary empathic connection yous share with that person via the family member. Therefor, it is more than just not seeing your own blood, but also trying hard not to think of her too, as "his" energy mat surface in your conscious mind. Empathic psychology always gets complicated. Since it's not just our own mind we have to deal with but everyone else's as well.
The best advice I can offer is to mindfully connect with your own family member and block out the person in question. This can be done in many ways. However, I would first suggest that you try it distantly before in person. A good distant exercise usually consists of just that - attending to the target person and blocking out the peripheral (the "sociopath"). This is good practice, and unless he is empathic too, it will work as a way of imagery utilizing what is know in psychology as exposure plus response prevention (often used for OCD but also can be used in extra-sensory perception experiences as well). This is good practice distantly as long as you do not try to connect emphatically with the sociopathic individual. That energy is often chaotic and uncomfortable to experience - also difficult to shake off. Other people may offer advice in how to "shake off" bad energy. My advice is to visualize connectors coming towards you and to visually and actively grab hold of each connector and rip it off. Be sure it is coming from the sociopath and not others that you want to be connected with or it can lead to other problems down the road. Either way, I would be certain that it is the person;s energy/thoughts/ strange emotions and not your own perceptions of him. Discernment is key here as in any situation like this. When you are ready for a visit, you may want to try various shielding techniques as well that I am certain many members of this group could share with you. These are difficult experiences to go through and true sociapaths can make any empath uncomfortable when perceiving their current mental state. Perhaps, this is a message for you in a way to subtly inform your family member of your initial perceptions of this person. definitely something to mull over for a while - but not too long. There has got to be a reason for our gifts, use yours wisely and good luck.