Generally, mum and daughter pairs are very stable, as the hierarchy is clear.
However, if you rehome any piggy (baby or not) from a doubtful background, you have consider these points, even more so if you are new to guinea pigs:
- any sow over 4 weeks old could potentially be pregnant (that in consideration that babies should ideally not be rehomed before they are about 6 weeks old/400g, but any boar babies need to be removed at 3 weeks old or the next generation could be already on the way). The risk of things going wrong during pregnancy and birth is noticeably higher in very young and in overbred sows.
- the guinea pigs need a 2-3 weeks quarantine and a thorough vet check, as they could come with mites, lice, fungal or other health issues. Are you up to medicating and/or bathing very skittish piggies (be aware that most backyard breeder's piggies have not had much human contact as a rule) and dealing with fungal issues like ringworm that can spread to humans and other pets?
- the mum's health depends very much on how often and how carefully a piggy has been bred; long term overbreeding (especially back-to-back pregnancies) can have a short as well as long term impact on a piggy's health.
That said, I have a five year old that was rescued during what was most likely her fourth back-to-back pregnancy. It has taken me months of tlc and a good diet to bring her round, but she has never had any major health issues, apart from developing cataracts. But her last daughter, who I adopted with her from a rescue, sadly died just after her second birthday from acute heart failure due to uncontrolled (in-)breeding.
If you are not sure that you are up to coping with any potential issues, please consider rehoming from a good rescue instead. You can be sure that all their piggies have undergone a full quarantine and pregnancy watch and have been carefully bonded; they are only put up for adoption when they are fully healthy and sturdy enough. By rehoming from such a rescue, you will incidentally make space for more piggies to get the necessary care from experienced people who are prepared for and used to dealing with all those above mentioned problems. If you buy from a backyard breeder, you encourage more breeding in the same conditions.
Here is the Piggy Bank map of recommendable (vetted) rescues that we can vouch for you not to have any nasty surprises.
https://maps.google.co.uk/maps/ms?msid=209994852075231951564.0004b8fd9391b4257d8eb&msa=0
