Fractional ownership is also possible without having to buy through a company. In fact it’s more common – i.e. when a husband and wife each own 50%.
The local rates (IBI) will be charged to one person. You should then settle up privately. For wealth tax and income tax you need to submit individual returns, and yes, the value is divided in proportion to your part, i.e. 25% if 4 equal parts. However best you check the detail with a Spanish tax advisor.