If you believe that you will have $208K in long term capital gains this year, then yes, you need to pay ~15% of that amount in estimated taxes. This would mean that the value of the home increased by at least $618K since the date of death and the gain is being split three ways. As we said in a previous thread, you will get a K1 from the LLC that tells you exactly how much of the cash you receive from the sale is capital gain and how much is return of basis.
You might actually owe a bit less than 15% though. It depends on all your other income, whether you are married, and if you take the standard deduction; but 15% is a reasonable estimate and if you over pay, you'll get a refund when you file next April.
Since this money is arriving in Q3 or Q4, make sure you keep good documentation showing the date that you received the funds. When you first do your taxes, they will probably show that a penalty is due because you didn't pay equally throughout the year. However, you can use IRS Form 2210 to show that your income was received unequally throughout the year and you did pay the tax due in a timely fashion.