Good Morning,
Sorry you are having an issue with one of the dogs. It is really hard to tell you what to do because ever aggressive dog is so different from the next. You gotta just kind of see what he responds to.
(but none the less, here are some suggestions you can try.)
I would first contact the owner and let them know what is going on. See if they have ever had this problem before if they have any suggestions.
Depending on what you are doing while the dog is snarling and growling at you, try doing the opposite.
Example: If you are trying to pet the dog, walking slowly up to the dog....... than try to completely ignore the dog. (although your nor really ignoring him, you actually need to pay attention to his ever move but do not let him know you are.) Do not make eye contact, pretend that he is not even there. Let him come up to you.
If that does not work or you already tried that yesterday than try giving him yummy treats. Something special; chicken is always good and easy and will not upset his tummy.
You mentioned that he bite your ankle.... I would make sure that there is always a barrier between yourself and the dog. a Baby gate works well for this also.
Depending on how long and what you are doing at the house, you may want to mentioned to the O about using a baby gate so you are able to spend time in the same house with the dog but just not in the same room with him until you feel comfortable.
But again, I would recommend contacting the owner and lettering them know the situation. They may have ran into this situation previously.
When you do talk to the owner make sure you are CLAM!! You do not want to worry the owner. You need to portray that their dogs on in good hands and that you are capable of handling her dogs. The last thing you want to do is to freak the owners out. So make sure that you have options on how you feel comfortable moving forward with these dogs, in the event that this has never happen before. If that is the case, keep in mind that the owners main concern is going to be that her dogs are being taken care of, that they are safe and loved.
Best of Luck!!