Is it normal to love multiple people?

You are fine. Even if you had a fling with her so what. It is not as if it is for sex, it is for love. Do what you want in life. I love several people dearly only most of them are unaware. That is life! Love is what it is all about. You can't love too much! Personally I am proud to hear you.

I think so. We are socialized to be monogamous but biologically designed to be the opposite and I am not talking from a purely physical standpoint either. I think one could possibly love multiple people simultaneously. Not weird at all, though may certainly complicate your life.

In what sense might it affect your relationship with your wife? You describe this thing as a 'trio'.

You don't like the idea of your sister-in-law being with anyone else? Is that what you mean? How strong is your relationship with your wife do you think?

And how is this 'the same kind of love'? I have felt great feelings for my in-laws, and wondered what would happen if we were to part, but this is a different kind of love. I would call it more a great affection.

Same kind of love? Do you want 'relations' with her?

I love my lady and all of her family, but in different ways. Don't want an intimate relationship with anyone else.

I love all my own family, and in different ways entirely again.

I truly don't think you have anything to worry about here. Why does it trouble you?