Although the Steen castle (by the river, just beside downtown Antwerp) is closed, the walkway around it passes a lovely plaque thanking the Canadian regiment which liberated the port and the city. I seem to remember that Canada is mentioned on some plaques inside the Brussels Cathedral, but Amsterdam and Antwerp are much nicer city visits. Note that Antwerp has a brand-new port, outside town, so I don't know how much of the old port is still authentic. (I think this is by the MAS Museum (viewing deck on roof), but maybe that was just the fish port? There did used to be old stone urinals (out in the open) beside that port! Don't know if they are still there. There is a historic warehouse (now a mall) across from the MAS museum, and a historic sailors club, now a restaurant (?) a few steps more. I haven't been to the newer Red Star (shipping) Museum, but that would presumably have war material.
The KMSKA (major, important art museum) is still closed for renovation. But on the pavement in front (left side, I think), there is a relief plaque in Flemish/Dutch about either the bombing or the shelling of the city. I'm not talking about the huge bronze piece of art that makes a reflecting pool in front of the main entrance steps. This is a very clear war inscription I'm talking about.
If you are in Antwerp on a Sunday, and don't have another plan, you might go to the Volkmuseum Deurne, an obscure, country-barn sort of place, behind a bar. It's got so much old junk in it that there might be some things (like the Crown Cork and Seal factory material), that your FIL might rember. And you can have a beer at the bar, the something-or-other Parrot. The Antwerp town hall is only open for visits on a guided Sunday afternoon tour, tickets at the TI. Maybe there are some plaques in there. Most major buildings in town, like the post office and rail stations, have memorial plaques for employees who lost their lives.
Your FIL may have forgotten about it, but the public pedestrian tunnel (1933) under the river is a major old public work, and probably was a shelter during the war.
Sorry, this is not major stuff, but I happen to have seen it.