Lisbon/Rome/Barcelona/Malta - is the weather any different?

I would not visit any of those in July. I am heat-averse and after 5 summers living in Rome, I am done with travel to hot locations in the summer.

Northern Italy, in the mountains, Scotland, or maybe Scandinavia, have some appeal to me, were we to go to Europe in the height of summer.

I am also a heat-averse, and to an ever larger degree humidity-averse, traveler and to be honest, if I were traveling to Europe in mid-July I would also not choose any of those destinations. (I wouldn't even choose Paris or London to be honest, because while they're normally pleasantly but not excessively warm in July, when there's a muggy heatwave those cities are difficult -- I'd be in Scandinavia or a high-altitude location).

However, I realize that you may have your reasons for picking your locations, and of the 4 you've picked I would pick Lisbon, which is likely to be the least muggy of the four cities. I know you said checking the weather online is not that helpful, but I would like to point out weatherspark -- it doesn't just give you average temperatures, but also how muggy it's likely to feel, comparisons to other cities, and other descriptions that give you a more well-rounded feeling of what it's like to be there.

The other thing is that Barcelona and Rome in particular are likely to just be absolutely jam-packed in mid-July, and I know from experience that being in too many overcrowded places can just exacerbate any climate-related discomfort you're already feeling. For that reason alone I would stay away from those places.

July is definitely one of the most busy months in Barcelona, it can also get quite hot/humid during the high summer months too. Also note that in Europe, Air Conditioning is by far not a prevalent as in the United States, many hotels, shops, restaurants may not even have AC. With one week, consider visiting Northern Spain aka "Green Spain" instead, summer is the perfect time weather-wise to visit.

I wouldn’t go to any of these in July.
Lisbon will be very hot, and it is hilly, you will be miserable.
If I were to travel to Europe in July, I would pick Switzerland or Northern Italy, lake Como area.

Let me preface this by saying that I like hot weather and being warm. That being said, and having been to Rome three times in the summer, it was too hot even for me. Finally, by the third trip, I dealt with the heat by getting up early and not over-scheduling my days and getting sightseeing done by around 1 PM and the spending the afternoons by the pool at our hotel. If you can do that, the heat will not matter too much. If you cannot do that, it will be exhausting.
I have not been to Lisbon (going next week) or Malta so I cannot speak to them. I have been to Barcelona 4 times, three times in the summer and once in November. November was way better but if you have to go in the summer, you have to go. Barcelona can be very hot but at least you have beaches nearby and again if you pace yourself, it could okay. I find Barcelona to be a less overwhelming city than Rome and because of that, it feels more manageable to me in the heat.

You are going in July to what is equivalent to Miami, Dallas, Phoenix, or St Louis and want to know which will have 'manageable' heat.

I doubt you will be happy with any of your possibilities at the time you plan to travel.

I see 2 choices-- go somewhere else or accept it will be HOT.

Lisbon usually has a cooling breeze, so it would be the most bearable of your options. Porto is a few degrees cooler.

Malta is a busy beach destination and therefore much of the better accommodation will have already have been taken. Malta is likely to feel the hottest of your options.

Got it, Thank you all very much for all the help!

If you look at lat/long coordinates, Malta is wayyyyyy down south. It was unbearably hot for me even in September. I would go if staying in Gozo instead in a farmhouse with a pool. That pool would get used daily.

I would pair Malta with a trip to Sicily in Spring or Fall instead.

Based on your first paragraph, none of those places is gonna be good for your family. Malta's a rock surrounded mostly by deep water. Gozo has sandy beaches. I suspect Barcelona's beaches will be very crowded - as the rest of the city will be. Lisbon and Porto are very hilly. Trams are packed like sardines with no AC. The metros don't go to many places. The only perk is that the water's likely to be on the chilly side, since it's the Atlantic, not the Med. Rome's not even on the beach and it's built on hills.

For weather data, look at this site where you can get daily weather conditions for the past 10 years for most cities.