It's easy enough to grow citrus from seed. Best advice is to use the freshest seed. Old pips have hardened the seed coat. I've heard that some folks will actually peel most of that seed coat off to ensure germination, but I haven't done that.
That's the good news. Another bit of good news is that with the grapefruit that sweet, chances are the seeds were really mature, because that's one of the main reasons home harvest of seeds fails: we take them from immature produce that may be at peak eating, but not quite ready to go forth and multiply.
On the bad news front, it will literally take years for you to get fruit from these. You'll probably see flowers in a couple of years, but they won't set fruit until the tree is a certain size.
Growing citrus in pots is actually a bit more complicated than most people think. Big box stores have a citrus potting mix that is actually detrimental to good drainage because it will compact too easily. It's very easy to overwater with waterlogged roots, or underwater, or not keep the roots warm enough, or not acclimate them to conditions, etc.
There are plenty of sites with citrus specific info out there. There are actually people far north of us that grow citrus and get fruit from their trees in pots, hauling them in and out of greenhouses. Citrus is also such big agri-business that there's data on every aspect of growing.