is it ok to leave two yorkies home alone?

In my book, no adult should be left for over 4 hours on a regular basis, if only because expecting it to 'hold' for longer, could build up kidney problems. No puppy should be left for over 2 hours. In both cases, especially not shut in a crate.

It's marginally better for dogs to have canine company, in lieu of their owners, but only just. And with two bitches, terriers particularly, it's always possible they could have a fight.

If nobody is going to be home during the working/school day, you need to find somebody to come in and let these dogs out or get them into a day centre. Dogs left alone, even with canine company, can become distressed, bark/howl/be destructive and noisy.

Add - Strangely, read this question which has just been posted, if you don't believe they might fight ....... https://uk.answers.yahoo.com/question/index?qid=20151011235707AA8uiL3

Separated yes. Without constant supervision they should be contained and separated. And I agree with V2, not for more than 3-4 hours.

Yes if they are both potty trained properly.

That will all depend on whether the two dogs get along well with each other all the time.
Chances are, they may not, especially being the same age, gender and also siblings.
Toys can be a bone of contention if left around and petty squabbles can get out of hand if no-one is around to supervise the dogs.
Leaving dogs all day alone is really not wise as anything could happen.
Unless you are 100% certain that the two dogs are compatible under all circumstances then you would be silly to risk leaving them together for so many hours. Jmo.

I think you should take it with you