My sister and I shared a room, so we used our bunks and I used my elder sister status to keep the top bunk til we unbunked them.
When my stepdaughter wanted one we got one used that had a twin on top and full on the bottom - so she could have sleepovers in her room with her best friend or cousins. She mostly used the bottom bunk. The top became a catch-all.
If you have two kids, I think it's likely that the top will be used, but I think you can't have the 5 yr old up there yet.
Get beds that can also function separately and you'll be fine either way. When SD got tired of the bunk, we eventually gave it away because it was hard to sell people on the beds that couldn't stand alone. It was also an awkward footprint.
And invest in a good wooden set. They last and last and can be used later. So those are my 2 big suggestions - get ones that function solo and get nice wood.