5 Month old kitten and mother in heat

Hello Everyone 

So long story short my nephew moved in over the summer with his female cat under the condition that she would be fixed.  Well lo and behold he never did and I found my male cat (now fixed) mounting her. Several weeks later 5 kittens! Now I did give 2 away to a good home and kept 3 males. The kittens were born November 1st  and we are now approaching April in a few days making them 5 months. I told my nephew he needs to get her fixed ASAP and he plans to do it this week.

My question is it seems that mamma is in heat she is walking around meowing and keeps biting the kittens, I am worried that because they are just reaching sexual maturity that something will happen BEFORE she gets fixed this week. Now the kittens seem to be ignoring her  playing with each other and trying to nurse from her (which they haven't done in a month or so)  but I am nervous as to what may happen when I am not home. 

Male kittens tend to not be fully aware and interested in females until the year mark. Not to say they can't; just that they are less likely to. Too get into the graphic, they don't start developing penile barbs until about 6 months and they aren't fully developed until 1-2 years old. My theory is that until they are fully developed the male is less likely to be successful and less hormone driven to mate. 

Assuming she is 100% for sure getting fixed this week even if something was to happen there wouldn't be enough development to prevent a spay unless you have strong feeling against a spay/abort. If you want to be completely sure nothing will happen separate them. Mom probably doesn't have much tolerance for the kittens if she is in heat anyways and would likely be happier without them bothering her right now.