Guinea Pig Mating

Question
Hello
We are new guinea pig owners.  We purchased 2 guinea pigs for our sons about 10 days ago. We did research guinea pigs before we acquired them, but we did get them from a pet store that apparently sexed them incorrectly.  We thought we had 2 females BUT 2 days ago the larger of the two started with the loud purr and hip swagger and rubbing against the other one.  Well, lo and behold the little guy mounted her and has done so many times over the past day or so.  So, I am safe to assume I have a little boar and a sow?!  And that we will be the owners of several more pigs in about 2 months time?   

Also, should I be at all concerned that the female could have already been pregnant prior to our ownership?   I am just very concerned about being a responsible pet owner.  I am sorry if this is a stupid question, but WOULD AN ALREADY PREGNANT SOW GO INTO HEAT?  Or am I correct to assume that she is likely a virgin and is likely to only give birth 60-70 days from now?  

I plan on having the little guy neutered ASAP (in the next week or whenever the vet can get us in!)
Once he is neutered, is it safe to leave him with the mother (and with the new babies?)  Also, I am aware that her male offspring could impregnate her after 3 weeks so I will have them properly sexed and the male(s) neutered.

I am just glad we are in the position to care for them properly as more than 2 was more than I bargained for.

Answer
Shannon -

First, let me apologise for the delay in my response.  I have been seriously ill for the past week and have been unable to respond to any emails.  

First, by now it may be a moot point for me to say this, but I would suggest for you to have him sexed by a reputable breeder or a vet before you do anything else.

There is a concern that the female could have been pregnant before you got her, but they cannot be bred while pregnant.  

It is safe to leave them together, although I would remove the male shortly before birth, as he could accidentally trample or otherwise harm the new pups.

I hope this answers all your questions, and once again, I'm sorry about the delay in response.  If you have any more questions, please don't hesitate to contact me again.  Good luck.

Lorena Kerr