Thank you for your question!
Many parents have successfully homeschooled children who fell into the 'only child' category. I am assuming from your e-mail, that you are concerned with the social aspects of your grandson's education. The social aspect of homeschooling is important, yes, but not crucial to the child's education. However, here are some suggestions which you could consider for your grandson's socialization.
Because homeschooling is becoming more popular amongst families, there are usually various homeschooling groups in any given town. There are, perhaps, homeschooling groups in your area, in which you and your grandson can become involved. Many homeschooling groups will have regular gatherings, field trips, classes, and other interesting activities that they do as a whole. This gives your grandson the chance to meet other homeschooled children, and maybe make a few friends his age.
Another way in which I would encourage your grandson to socialize, depending on his age, is to become involved in your parish. There are probably many activities that your parish does for the community, such as helping out at the soup kitchen, cleaning the church, etc.
Also, I would highly encourage your grandson to become involved in the community, according to his interests. For instance, most local libraries usually host learning events, as well as other fun activities especially during the summers. If your grandson plays an instrument, it would be natural for him to join a community band or orchestra. If your grandson enjoys sports, there are many opportunities in the community to become involved.
I hope that this helps give you some ideas!
God bless you and your family!