2 things here: First not what you asked: You need to prune the main trees. Rule of thumb is that on each branch cut off 1/3 of each years new growth. You do this before the next years buds open. (find out when is best in your areas I'm in Iowa) you can see where each year starts by what looks likes a junction, or some might compare it to how the skin looks on your knuckles. I won't go into the the why's and ect of pruning in this thread. You have some time to read up on that. But read here not the web in general. Here is what you 'can' do on the suckers. Wait until pruning time, then take your time in getting those removed, dig around them with your fingers and see how much root you can get with it without scratching the main trunk or a large root . cut those off 4" above the ground line and replant them in a pot or in the ground. It will need very damp soil to start, but don't let it be waterlogged, that will drown it. So if you get one or more to retake you can bud graft in the fall from your trees or other apple tree in your area. None of this is complicated and you have time to get your mind around it.

you have a lovely shaped apple tree there and it looks like your grafts did well. I am not an apple tree pruning expert and I hope someone who is will reply to this post for you. I would be inclined to make sure that each graft is growing correctly and prune accordingly. I have a vigorous Hudson's Gold Gem graft on an old apple tree that I think needs to be pruned just to get rid of an odd crotch angle that is developing. These kind of bad habits are sometimes overlooked in the excitement of all the new growth.

Certain types of galls will have an exit hole where that the gall wasp uses, making it look like an insect nest.

Alternatively you could buy rootstocks, $2.75 - $3.75 each and graft cuttings from your tree. Cummins Nursery sells onsies. There are many sources of info on the web including this video . I prefer a text with pictures article like this one. You need a knife, I used a retractable safety knife and grafting tape that I bought for $5 on eBay. Since your source for scions, the cuttings, is from your tree you can cut them from your tree to match the diameter of the rootstock. I use a crescent wrench to choose the exact spot to make the cuts. This will ensure the cambriums line up. Clean up your tools before you start with rubbing alcohol. The biggest expense is the shipping which last spring was $22.50. The rootstocks only ship in the spring so you'd want to get your order in just after new years. The cuttings should be done in mid winter or as long as your tree is dormant. A suggestion I could make is to get two rootstocks, do two grafts and plant them in the same hole... maybe a foot apart. Later choose the healthiest and cut the other. The rootstocks are numbered according to size. M9 is a dwarf, m7 is a semidwarf, m111 is a semifull rootstock. The M stands for where the rootstock series was developed. That one is Malling, in England, those with a G are Geneva in NY. The B's are a Russian rootstock. Generally the numbers match or are similar. I have used M7's and M111's. I also did a combination of the two to get a semi-dwarf tree with a larger root system. I would think you should select a rootstock to give you the length of the espaliers you want rather than deciding on a basis of height. In my soil, raw clay I find that a semi-dwarf tree seems to grow more like a dwarf. And I find that in the first couple years you shouldn't be disappointed with slow growth.