Hi and welcome! Sagos are very slow growing and take some years to "trunk up". Yours look very healthy and the bigger ones are starting to become little trees. Give them a little encouragement with a small amount of palm-specific fert, and they'll put on nice growth through the summer.
You can trim off some of the lower fronds if you want to. They're very thorny, though so be careful! I would think the dogs would steer clear of them because of their thorns.
