My dogs won't eat out of bowls anymore after my sister's dog came over and ate out of one?

Yes they will.    You offer the food in the bowls, and only in the bowls.   Stop giving into their fussiness.    They will eventually get hungry and eat.

It may take a few days, but they WILL eat from a bowl if you just simply stop dumping it out for them.

Just put the food in their bowls & leave it down for them to eat.  They will eat when they are hungry enough.  A dog will not starve itself if there is food available.  They will eat out of the bowls when hungry enough.  They may not like the food you are buying.  If you switch foods, take about a couple of weeks in changing from one to another, gradually adding more of the new & less of the old but take the time to do a proper switch or the dogs will get diarrhea from a sudden switch.

 Then maintain feeding them in their bowls when they get hungry enough they will eat out of them again.

Rubbish......If the dogs are hungry enough they WILL eat out of anything including another dogs bowl.

Don`t feed them ANYHING, not even a treat, for 1-2 days + and then watch them eat out of their bowls. 

NO healthy dog is going to deliberately starve itself to death, just because its food is in a bowl.

If this is likely to be true, get new dishes for your dogs to eat out of.   You say dogS, has this invasion on the part of your sister's dog, affected ALL the dogs you have?   I find that very odd.

If this is true, keep at it - eventually if both/all of them are hungry enough they will eat out of a bowl, as they should, rather than on the floor.

maybe theyre afraid of the other dog's germs

WHY would you do anything so UNSANITARY... as to DUMP the dogs' food on the GROUND vs simply putting in in a new bowl?  You could use anything in your cabinets (a pie pan, cake pan, paper plate, etc.) then if reusable =sanitize it in the dishwasher.  That would tell you - then to... BUY new bowls or to CONVERT something you have, for the dogs to eat out of.

REAL SIMPLE => The dogs WILL decide to eat (at least out of a new bowl) WHEN they get hungry enough.  (No dog will starve itself to death.)