Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
Deeding the house to all four of you is the correct way to do this. Should the house ever be sold (or if one of you buys the others out) the basis will be 1/4 of $515,000 each or $128,750 each. Any sales price above that will trigger capital gains taxes. However, if one or more of you live in the home as your main residence for at least two of the five years prior to the date of sale there is a gain exclusion of $250,000 to that party ($500,000 if married filing a joint return in the year of sale) which will be deducted from the gain before there is any tax. Then the highest capital gains tax rate is 15%. Although any taxable gain will likely be below that rate, it is always safer to estimate at the highest rates. You are also able to include in basis any improvements made since you took ownership as well as deduct selling expenses (realtor, attorney, etc.)
For an example: (per owner)
Basis to begin $128,750.
Basis at time of sale $140,750
Selling price $200,000
Expenses of sale 17,000
Adjusted selling price $183,000
Basis at time of sale 140,750
If the home served as the primary residence (see above) there would be no tax since there would also be an exclusion sufficient to reduce the gain to zero.
However, laws do change. Tax laws are not different in that regard. You should investigate tax changes just prior to selling the home to be current on the laws at that time.
How do you calculate improvements? Do you have to keep receipts?