The twins share the en-suite, the other two have normal bedrooms and then you have a spare room/snug/study.
It's kind of insulting to make children share (unless they're tiny and/or desperately want to) when you have enough rooms for one each. Spare bedrooms/studies are very nice to have, if you have capacity, but they don't usually go with the territory of having four children.
As for those saying that it's only because the twins are the closest in age that they're being asked to share and not just because they're twins, erm, how do you think they ended up being the closest in age?! It's a circular argument. Absolutely not getting at OP at all, as loads of people would instinctively do the same, but she said 'DTs11, DS8, DD5' - putting the twins as one entity, to the detriment of mentioning their sex, which is very relevant here - and not 'DS11, DS11, DS8, DD5'.
I'm not a twin, but it must really be annoying to be constantly grouped in with one of your siblings (or your only one) as if you came as a pair. That comes later, as an adult, if you choose to share your life with somebody and not just by default because you happened to share a uterus with somebody before you were born.
I don't know how old the house is, but I'm incredulous at how house developers design properties just to look good on a spec sheet for sale rather than to be practical to live in long term. Fair enough that you'll get some families with one or two children wanting a large house with good sized bedrooms for use as such and also one or two smaller rooms for studies/storage/guests etc - but it seems completely beyond the wit of developers to consider that a lot of people buying a 5-bed house will be families with four children, so they might just want a master bedroom with en-suite and then four others of an equal size and maybe an extra family bathroom, so you still have the option to assign bathrooms according to need irrespective of the bedrooms, if you choose. Otherwise, one child gets a big room and an en-suite whilst another just gets a tiny little box room - to the extent that, as in this thread, people propose two children sharing one room whilst another goes largely unused. What if OP had triplets or even quads?!
An awful lot of family houses seem to be designed with two rooms for adults and then just slotting the children in wherever. Yes, some will want that - HMOs, grandparents living with you or one much older child than the others - but I wouldn't have thought that would be the majority.
Seriously, it should be the house planned to suit the occupants, not the occupants rearranging themselves to suit the apparently unalterable layout of a standard house.