the maximum you can spend is 6 months on any one trip in the uk, thou i don't think law, but could be policy of the HO, and many Immigration officers think you should not spend more than 6 months in any one year in the uk, so that's one of the main reasons for refusal, and because of this, as mentioned in your refusal letter they are not satisfied your coming as a visitor.
also when you said you was coming for 2 months, and you provided evidence that your sister could support you for that time, that's what the case worker based his decision on, the evidence at that time, and you staying 6 months would have need far more financial evidence, so they suspect you could have been working
no way 95% of appeals are won, that depends on the reason for refusal and the evidence you have, more like 45% are won if that.
and no i don't think the HO would care about your sister going thru a divorce, to them it's not the most compelling compassionate circumstances
good luck, i'm not sure you would be successful, but you never know![]()