Pour your advise please - Relationship issue

Dear ladies

I have discussed my original issue in a separate threat, and got valuable responses from you all. For those who never visited that thread, pls read it here http://www.indusladies.com/forums/parents-and-siblings/249929-why-me.html

Coming to the newer problem

One of my mom's cousin's wife is related to my SIL's mom. This aunt is living in our city, so she represents all our family events without any fail. Our other close relatives stays in other states, countries so that they visit only on special occasions. So this aunt is the more close family member to us to the eyes of others. But we never treat her so special, but respectfully within her limits.

According to my SIL, this aunt called them once after the engagement, and told them that my brother is a sweet boy, but myself and my mom are evils. She allegedly added that I and my mom never wanted to get him married as we wanted to enjoy his earnings. He built my house, and still repay the loan for it. He still bears my family expenses, and my kids are under his responsibility. By showing fake love and affection, we drain him, and hence we didn't want to get him married. However she said that my brother liked this girl and fought against all odds to marry her.

She allegedly said that most likely my mom and I will separate the couple after their marriage, so the bride needs to be prepared for it. She even brain washed the bride over phone calls, and advised her to be tough, send us away from her life after marriage. She promised them that she can turn my brother towards them, as none of us live in our native city, where our brother lives. She lives close by.

By being too friendly with her, my SIL and her mom danced as per her tunes. They ill-treated us even during the wedding, but we gave them the benefit of the doubt by thinking they must be upset of leaving her DD.

Then we actually doubted my DH, as SIL said it was my DH who gave all the bad tips about us, and advised them to be careful with us. We believed her, because DH never shared a very loving relationship with mom. In fact, there was a minor issue between DH and mom in the past. I even fought with DH for this, but he promised on my son saying that he never talked to them as such.

Later, we came to know through others that this aunt has told them even our silly jokes during wedding times in a sarcastic manner to hurt the egos of the bride family. She turned all of them against us.

Now I went to this aunts house with my SIL and mom to ask why did she tell all such bad things about me, which is not true.
To which she accepted the jokes and minor matters, and said she just shared the jokes but nothing else.
She accused us for believing our SIL, who is playing double game here. She said some nasty stuff about me which my SIL said to her. She even tried to beat my SIL in order to stop her from further saying things against her. My SIL agreed, and said she was angry on me, and misunderstood me for everything because she was badly brainwashed by this aunt for a long time. So she couldn't think clearly at the beginning, but now she understands everything. In fact, I financially helped my brother but he never helped me. All issues came against me, because SIL and her family believed that I drain him.

With the same doubt, I see my long time personal problems with in laws. Because my MIL is too close with this aunt. This aunt has told me so many stuff about my in laws, as too project them as my enemies. By trusting her, we too uttered some bad things about in laws (which are true by the way). All I say here is, that I suspect she must have been the reason for my rifts with in laws in the past. However we are in good terms now.

Now it is like broken glasses. After knowing my SIL had said so much negatively about me, and never was ready to bare my 1/2 day visit to her place in the past, I couldn't mingle with her closely. I developed hatred towards her now.

This is how I could not wholeheartedly accept my in laws now. They are too good to me, but my past haunt me and I suffer in between. Same applies to my mom.

If the problems are based on misunderstandings, and could have easily avoided, but became too nasty fights because of this aunt, then how come we forgive her?

What can I do after knowing all this?