Will the pattern fade on my old Royal Doulton D6141 china inherited
from my 95 year old mother in law if I wash it in the dishwasher on
regular wash cycle on a regular basis? How about using the delicate
cycle? Will the pattern fade if I use the dishwasher to clean my china
occasionally? Will the pattern fade if I use the dishwasher for a
period of 2 weeks while I have houseguests? If not, should I always
use the delicate cycle? Really need answers to each of these 5 questions.

From the Royal Doulton site:

Washing
China can be washed in a dishwasher - at a maximum temperature of 65
degrees centigrade.  When washing by hand, avoid the use of scouring
pads and abrasive washing detergents.  Most stains or hardened-on
particles can be removed by soaking the item in warm water before
washing.  Really stubborn stains can be removed by soaking in a mild
bleach solution for up to one hour.

http://www.royaldoulton.com/website/content/faq.jsp?bmLocale=en_GB#13

or

USE AND CARE INSTRUCTIONS
Royal Doulton has produced durable bone and fine china products that
will last for many
years to come if cared for properly. They?re also dishwasher safe.
Gold or platinum trimmed patterns should not be placed in a microwave oven.
~ Do not put the pieces directly on a hot stove burner or flame.
~ When used over an alcohol burner or canned heat, be certain the
bottom surface is covered
by sufficient liquid to distribute the heat evenly.
~ If refrigerated, let warm to room temperature before placing in an
oven for baking.
~ If frozen, let thaw to room temperature before placing in an oven for baking.
~ Use only non-abrasive cleaners or scouring pads.
~ Do not drop or strike against hard or sharp surfaces.

From this source : http://www.giftcollector.com/PDF/ROYAL_DOULTON.pdf

So its looks like you should be ok.

I would try to get more information about machine dishwashing older
china before doing it too often.  Dishwasher detergents are quite
strong and there could be a chance that the colors would fade.
I would also be very careful about heating plates, serving dishes in
the oven. The glaze may "crackle", perhaps also the reason why max.
65°c is recommended for the dishwasher.

I am in the tableware business and it is absolutely NOT recommended to
wash any tableware that does not say "dishwasher safe".  Even more so,
you should not put china in the dishwasher that has any gold or silver
trim, or china that was made when dishwashers weren't.  They simply
cannot handle it.

Don't do it!  Electric dishwashing detergent has lye in it, which will
eventually damage the plates. If you want a helping hand to wash your
dishes, run the dishwasher with no soap (which will get the plates
clean of food, but not of grease) and then you can quickly wash them
by hand with soap.