I assume you mean GWB and GHWB. I would think those public affairs involving past heads of state, Trump would "have to be invited" and "have to appear." He'd handle it fine. He'd pretty much have to appear, it's more than a family decision.
Trump isn't going to deliberately insert himself privately where he isn't welcome, and he is obviously not in the Bush family orbit.
Actually Trump could do what Obama did when Scalia died, just go to the viewing.
Unlike the Clintons and Gores at the funeral Mass for Cardinal O'Connor at St. Patrick's Cathedral in NYC.