In the Netherlands, you'll probably have little to no problem in any major cities, from my experience people in the service industry (hotels, most restaurants, museums) speaks good English.
Bruges is touristy to the max (beautiful city center though), I'm sure it won't be an issue.
Bruxelles is harder to judge from that perspective for me but some of the popular districts for restaurants (Bourse / Beurs / The Stock Exchange, Grand Place or Sainte-Catherine) will have plenty of English menus / staff speaking english. Same for all the museums. I mean the city houses some UE and NATO institutions, it's fairly cosmopolitan. Maybe less so around Schaerbeek or something but it's probably not the part you're likely to go see. I don't think Brussel is noticeably worse for that than Paris, frankly. People are pretty chill too.
The biggest language barrier, according to the people there, is when you're a Wallon and you start entering the Flemish part surrounding the capital. Wallons are convinced a lot of Flemish speakers will stonewall you and refuse to acknowledge them in French or English even in train stations and such. Possibly overblown and a result of the longstanding tension.
In the Netherlands you can consider La Haye, it's a pleasant city even if for a couple of day. Go see the deers right outside the railway station. You can go swing by the beach if you want to. Same in Brugge, you're not too far from Ostende.
Amsterdam and La Haye have great museums too, and they must be out of renovation now. Bruges has good local beer (Zot and the rest of what their brewery do), decent museums, and a Madonna by Michelangelo in one of the churches.
The Thalys high speed train does connect Amsterdam to Bruxelles, and also goes to Bruges (though after a fork IIRC) but you can probably manage with just standard trains in most cases.
