You can't necessarily go by the figures they give you at seedbanks. Estimating a specific person's yield is impossible to do unless you know all the conditions the plants are being grown under (lights, humidity, temps, ventilation, soil, nutrients, the containers used, the person's experience ...) and even then it is somewhat of a guesstimate game - unless you've grown it before.
Second thing, those figures are not 'per plant,' but rather, 'per area.' For example, if they tell you 500 grams yield, that usually means 'up to' 500 grams per square meter (or some other area size.)
It's a little difficult to explain but, you need to use area to estimate yield because yield varies a lot by the size of the plant. For example, you might grow 25 smaller plants in that square meter and get 500 grams or you might grow 5 big plants and get 500 grams.
Given all these variables you see why it's hard to estimate a specific person's yield for a new grow. However, you are only asking about 2 plants so ...
After having said all that, I will guess anyway. :~) With 2 white widow plants (which is a good yielder - one of my favorites) you will probably get anywhere from 1/2 ounce to 3 ounces per plant depending on all the factors I mentioned, i.e., your experience, lights, nutrients, soil and so forth. Experience is a huge factor. So are lights. 1/2 an ounce would be for someone with poor lighting and not quite sure what they are doing; 2, maybe 3 ounces with decent lighting and growing plants of a reasonable size, without growing too big. (White Widow is short and bushy and tend to grow in a Christmas tree type shape. It can produce a LOT of bud when grown outdoors.) I have no idea how much experience you have, but often beginners think they are taking good care of their plants when actually they are doing many things that will decrease yield. Everyone (almost) gets better with time.
I have gotten 4 ounces out of a larger (to me) white widow plant but that was a rare thing because I tend to grow smaller plants in a sea of green type setup. I'm attaching a pic of my current white widow grow. They are 3 weeks old. (There might be a Haze or two in the pic also, not sure without looking, 'cause I've thrown a few of them in the grow. (They're younger.) Good luck to you - hope this helps.