That's a question for a competent artist to answer. I imagine it would be a difficult cover-up, given the size and placement. If it were me, I'd just start thinking about other tattoos to go around them. Were these done by the same artist? If you like that style, they could probably build a really cool cohesive sleeve from what you already have. Or just collect different tattoos around it - I honestly think they either way would look just fine.