An adult would not start growing as their skeletal structure is mature. Now children growing up in a lower gravity would tend to grow taller than those back on the homeworld.
Prolonged stays in a low g would have as you said, the loss of bone density, and loss of muscle mass, their cardio function would lessen, but that would not be an issue until they go to homeworld.
Lower pressure is the bigger issue, the pressure on Abwehr is three times higher than on earth. Basically three atmospheres, or the equivalent of being under 20 feet of water. So they would need some sort of breathing apparatus, or as you said a pressure suit, otherwise they would suffer from hypoxia, which can become fatal.
The effects are cumulative, but a short visit wouldn't be a problem.
Now if for example the Abwehran had an embassy on Yamatai, they would probably want to install gravity generators under their embassy to create their natural gravity to protect their citizens. Obviously there would need to be signs warning people coming in as to the change in gravity.