Why is the bread so dense and moist

Pinapple + gelatin should raise red flags.

Pineapple contains bromelain, a protease enzyme similar to papain in papayas. This enzyme when active will prevent gelatin from gelling. Heat will deactivate that enzyme. Canned pineapple is usually cooked enough that it isn't a problem.

If you are using fresh pineapple (or suspect your canned pineapple wasn't cooked enough) you should cook it to at least 65C to ensure that it doesn't eat your gelatin.

Protein-devouring-pineapples aside...

The gelatin mixture is going to be much denser than the whipped cream. The pineapples will be even denser than that. In order for the two liquids to stay mixed they will have to be well gelled. Make sure the gelatin mixture has cooled enough to be very viscous. When adding the whipped cream you should fold (even though the recipe doesn't say to).

To keep the pineapples from sinking you should cut them into smaller pieces. Additionally, you might let the mixture partially set before folding in the pineapple.

In his in depth review of pie apples, Kenji Alt points out:

Well, there's another thing that acid does: it strengthens pectin, the cement-like glue that holds together the cells of fruit. So looking at this arranged spectrum of apples is actually a pretty good indication of how well each fruit is going to hold up during baking. The further right along the browning scale, the firmer the apple should be in the finished pie.

This same affect will apply to baking apples filled with cranberries: you want an acidic apple, as they are going to hold their shape best when baked.

While I don't know the varieties available to you, he points out that the more acid the apple, the more slowly it browns when cut:

[A]cid can inhibit the browning oxidation reactions that take place in fruit flesh when it is exposed to the air. For this same reason, cooks will store trimmed artichokes in acidulated water—it prevents browning.

The slowest browning, and most acidic of the US apple varieties he tested was Granny Smith. This Whole Foods recipe for cranberry and almond stuffed apples concurs.

This goal of having a sweeter apple to counter-balance the cranberry filling is at odds with needing a more acidic apple to contrast with the cranberries.

Instead, you may be better served by adding sugar to the cranberry filling. Since both cranberries and apples are assertive flavors, they will stand up very well to a sweet filling.

Time and temperature for apples are pretty flexible. A survey of baked apple recipes shows options from 325 F (160 C) for about 45 minute to an hour to 400 F (205 C) for 15 minutes. The important thing is to take them out when they have become tender when tested by pushing a knife point through the body.