Looking at size of the query 88 seconds seems small 
. Jokes apart. If you see your plan you will see that 6 tables are used in reformatting using store index. If you see that these 6 tables are actually 3 tables but for 3rd and 4th select in your query. Thus your first 2 query with union ran fine but as soon as you added 3rd it went for store index for 3 tables and that took time. Same happened for 4th select statement. You will need to look into why it has chosen store index for query 3 and query 4.
I guess you mentioned that individual query gets executed fast. I would suggest that you simply insert each query's output into temp table and then do a union on those 4 tables.
Hopefully, it will help. If time permits I will look into query 3 and 4 to check why the store index used there.
Thanks