It is actually quite normal to maintain a breeding colony of a single male (the boar) with several sows. The other adult females are extremely unlikely to be of any danger or hindrance to either the young or the mother. 6 babies is quite a lot for a guinea-pig, their litters average about 3. The other adult females are not likely to be of any assistance.

Since guinea-pigs are born unusually well developed, there is usually little risk of individuals being neglected to an extent that it is detrimental to their well-being. However, babies which weigh less than 50g at birth may fail to survive. If you find that the mother is struggling to milk all 6 of the babies effectively, you can place a saucer of warm cow’s milk in their pen. You must watch, however, that they have access to this before the other adults, and also that the adults don’t become fat!

After just 2 days guinea-pig young can eat a little solid. This can be achieved by soaking a little brown bread in warm milk and placed on a saucer. Good luck!