The lottery rules in your state don't matter. You can split a prize any way you want to, because it's your prize. The only difference is whether the lottery writes multiple checks or if they give you one check and leave it to you to give others their share.
If you don't want to pay gift taxes, don't give away gifts that are worth a lot of money. That means giving them a share of the ticket, rather than the prize. Better still, split the cost of the ticket so that their share isn't even a gift. When you actually collect the winnings you should expect that the IRS will want proof that the others already owned shares of the ticket before it became a winning ticket. If you don't have a written agreement that predates the drawing, plan on paying gift taxes after you've already paid the income tax on the full value of the prize. You should also expect that the IRS will want proof that the agreement predates the drawing. Just because you write "July 15, 2007" on something doesn't mean the agreement wasn't written on July 21st. A court may rule in your favor based on testimony that you intended to share the ticket (or maybe even based on an LP post that is archived), but a formal, written agreement would be safer.
As long as you're concerned about gift taxes, how do you feel about estate taxes? Giving 15% of the current MM cash value to your parents could make their estate worth close to $7 million. Even if they're only 40 they could still be hit by a bus walking out of the lottery office after collecting the prize. If their estate was worth $7 million the IRS would get a large chunk before the remainder goes to their heirs. Since you're presumably one of the heirs, some of the money you gave them would come back, minus the cut taken by the IRS. That seems pretty silly to me.
That's why I would never give such a large share to my parents. If I wanted them to benefit I'd give them a smaller share and then I could give them a gift each year. If I'm married my spouse could also give them a gift, allowing us to make a combined gift of $44,000. They wouldn't have to pay income tax and we wouldn't have to pay gift taxes. If I had two sisters I could give them a slightly bigger share and they could make similar gifts. You could then potentially give your parents as much as $132,000 each year with no gift taxes, and no estate tax before getting the moneyback if/when your parents die.
Buying a house and letting somebody else live there can involve some serious risk for anyone. For a lottery winner it would be truly foolish. Suppose your sister is living in your house and she throws a party. Her friend drinks a bunch of wine. The wine you gave your sister as ahousewarming present. Then she falls off of the deck and becomes a quadraplegic who is unable to work and provide care for her 4 young children who don't have a father. She decides to sue and the lawyer looks for some deep pockets. Who do you supose has the deepest pockets around?Wouldn't it be better to give your sisters 3% each and let them buy their own houses?