If I’m the sole beneficiary to my moms life insurance policy is it taxable?  NO. 

Also if I’m going to split it with my siblings, does that fall under a gift tax?  YES if you give more than $15K per person per tax year so you have some  planning to do.  

Generally, life insurance payouts are not taxable.  There may, however, be some types of investment vehicles that are branded as life insurance but which have some tax consequences.  You would need to ask the company to know for sure (although this is uncommon).

If you give money to anyone other than a spouse, you must file a gift tax return if the amount of the gift is more than $15,000 per person per year.  However, no tax is actually owed unless your lifetime total of gifts is more than $11 million.  The gift tax return is used to track your gifts against your lifetime total.  The gift tax return is filed separately--it is not part of your regular tax return and Turbotax does not include it.