How close are you planning to plant them? Citrus will try to bend/lean around the banana to receive more light and may take an awkward shape. Also Bananas are water and nutrient hogs and grow much faster. In hot tropical climate the life-cycle of banana is about 18 months from a pup to 10+ feet followed by fruit production and then they die.

Azores +10C to +25C. Probably too close such as 1 m or 1,5 m. Dwarf bananas only that grow up to 2 m in height. Soil must be all purchased since this is all bedrock or lava.

You are in great climate zone plus a beautiful island. Someday I would like to visit. I think a dwarf banana may have at most 1m radius. So you can keep the citrus at 1.5m it should do fine, I am assuming you get a lot of Sunlight in that area.

Welcome to visit. It is a climate which could be called "cooler tropics" where instead of truly tropical 20C to 35C it is by 10C lower on both ends. Sunlight in reasonable amounts, especially further away from the slopes of the huge volcano, where less clouds gather, but can be some days in a row without it in winter when temperatures do not go above +18C. What I want to do is to plant a couple bananas between still very young orange/lemon trees that are planted about 3 m or even 2,5 m from each other.

If it were me I would go ahead and do it may be giving the citrus a bit more preference for light. You could also plant in a pot and dig the pot into the ground. So if you do not like it then you can move it. That is what I do with a lot of plants. We go from -15C to +35C and so the tropicals have to be brought in anyway. But in summer I dig them into the ground. They do much better directly in ground but pot in ground is the next best option and flexible too.

Yes dwarf you can do. Still I would plant them no less then 5-6 feet apart . It sounds like MED climate.