Well you should have gotten tax advice on this BEFORE you sold the house. The IRS will expect the sale to show up on your return because only your name is on the 1099-S.
Now the easiest way to resolve this is for you and the siblings is to complete your in full WITHOUT the sale ... make note of the bottom line. Then go back and ADD the sale and note the new bottom line. Subtract one from the other and divide by 3. That 1/3 is what the sale cost each of you ... so the each owe you 1/3 of the difference ... how you settle up is your decision.
