Most grandparents, even if they used cloth diapers on their children, wont be interested in flats, prefolds, pins, snappis, or covers. Some of our parents are even scarred with horrible memories of extremely bulky diapers, sticking their babies with pins, and leaky plastic pants. They may resist your cloth diapering ways and wish to use disposables while they watch the baby. Luckily, there are so many options out there that you can set up a nice little stash of cloth diapers for them to use that are as easy as disposables!
Ease of Use-To best prevent post traumatic stress for your parents (or in laws) when they care for your baby, you may want to help them out by supplying some very easy to use All-in-One (AIO) or pre-stuffed Pocket Diapers. Aplix or velcro closures will also help, as a dozen waist snaps can be intimidating to some (including your husband, but that's another story!). Also consider that arthritic fingers can have a hard time with snaps.
I have found that I adore the Tots Bots Easy Fit diapers for our own stash and as our sitter diapers. They are somewhere between an AIO and a pocket. The insert is always with the diaper, but it stretches out for easy cleaning. There is plenty of room for stuffing them if you need more absorbency. The aplix tabs are strong, easy to use, and make for a quick diaper change on a crocodile death rolling baby! Tots Bots have a pocket style lining without folds and layers for poop to get trapped in (a huge bonus in my book!).