Wondering are the Northern Pike and Muskies able to withstand warm water [26-29 'C]? Are the other smaller species able to thrive in such warm water?

Certainly, some of the smaller Esocids can take and thrive in warmer water. The redfins and chains my way are often found in very shallow, very warm water during the summer months. I'm not certain how they would fare ovr an extended period of time though. I can't really comment on the larger species since I have no direct expereince.

I have no doubt that Musky and pike could tolerate warm water for brief periods in the wild. This is something that can be observed as a fisherman. In large lakes during hot periods you'll find large northern pike in the deepest water available (with sufficient oxygen) only to venture into shallow water to feed. I think 84.2 degres F might be pushing it for Pike and musky. I would certainly be very worried about this temperature in the home aquaria.

I certainly find Grass pickerel in water at or around your low mark (78.8 deg. F.) but for home care I always try to keep the temps as low as possible without chillers. In my local area Grass pickerel seem to prefer some of the cooler water available. You'll find them in warmer water but the strongest populations can be found in water a little cooler than average. To answer your question more directly I would say pickerel do seem to prefer shallower (warmer) water than thier bigger family members. In the home aquaria I would avoid temps above 80 deg. F. for any extended period of time for even pickerel.

Muskellunge, at least in some lakes and rivers in the South, can tolerate waters uo to 80 degrees.

we have some muskie around here and water is pretty warm during summer,(middle TN) however they are usually pretty deep or near dams where the water is a tad cooler,

Northern Pike need the coldest water then muskies then chains and then the grass and redfins can tollerate the warmest temperatures. but I would agree with others in that even the pickerel don't seem to seek out realy warm waters. I have read that northern pike can not get larger than about 7lbs in farely warm water and get much larger in colder temps. This is why ohio stocks muskie instead of pike, most of our reservoirs are too warm for them and the places you do see pike they rarely get over 2 ft unless your in lake Erie.