Problem Statement:
How to identify the Max and Min date value in a row in SQL Server?

Code:
Here is a solution to identify Max and Min date value with the help of CROSS APPLY in SQL Server.

create Table FindMaxMindate
(
    ID int, 
    Firstdate datetime,
    Seconddate datetime, 
    ThirdDate datetime
)

Insert into FindMaxMindate 
Values
(1,'2018-01-26 19:14:07.587','2018-04-26 19:14:07.587','2018-12-26 19:14:07.587'),
(2,'2018-12-26 19:14:07.587','2018-01-26 19:14:07.587','2018-03-26 19:14:07.587')

Select ID,Min(Dates) MinDate,Max(Dates) MaxDate
From FindMaxMindate A
Cross apply (values (Firstdate),(SecondDate),(ThirdDate))B (Dates)
Group by ID

Drop Table FindMaxMinDate