This would be considered as a gift to your sister from her father mother and brother and since she is a major such income won't be clubbed in the income of her parents and thus you can clearly take benefit of slab rate and save some tax. This is tax planning.
Even if there is no tax liability you will have to prepare gift deeds showing the gift given to your sister and your sister will show them as exempt income from her relative. Also have a documented proof of gift which shows the cheque number through which gift was given so that if anyone asks you can show bank statement and gift to prove the gift given and received.
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