Unity of Possession means that each tenant has use of the entire property and not just some designated piece of it.
If the interest of the tenants is unequal, each still has use of the entire property.
Two people own a house as tenants in common with one owning 25% and the other owning 75%. Both have 100% use of the house. The one with the largest proportional share cannot exclude the other from use of any part of the house or lot.
Don't forget that any written agreement may negate this. The cotenants can agree that each will use a specific part of the house or use it only at certain times of the year but this is a separate agreement with respect to the tenants' rights.