Hubby doesn't love you. If he did, he wouldn't be cheating on you, and he certainly wouldn't be trying to move the other woman (and yes, that's what your sister is) in with you. What he really wants is to gross you out enough, to get you to move out, so he can have the home, and the other woman.
First, (and don't discuss this in advance) change the locks on all the entry doors, and don't give him copies of the new keys. Second, if you are foolish enough to still want this creep, tell him the price of admittance is he drops your sister and goes into counseling with you, as your sister is not moving in with you, and you are not moving out. Third, tell him that if he won't give her up, he will have to find somewhere else for the two of them to live, and he will have to settle for visiting with his kid, instead of living with him. Fourth, get a good lawyer. Fifth, inform your family that you will not be attending any family functions that sis is invited to, and tell them why.
Frankly, both your husband and your sister are crap. Dump both of them.
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau