Thanks everyone. It's nice to get the perspective of others.
I'm done and dusted with SIL. It's been exhausting and I am well and truelly over it and dh feels the same way. Whilst initially dh and I would have liked and god knows we tried several times to make her see sense and move on from whatever her problem was/is because we wanted her to get to know her nephews and be a part of all our lives in a positive way but we realise that 5yrs later and she is still carrying on and it will never be and now we prefer it to be that way TBH because our boys certainly don't need a person like her in their lives the way she is and we don't have the energy to try with her anymore.