The official Instagram app is available here:
If you don't see it on your phone, make sure it meets the minimum requirements.
I do not understand the question completely, but if you are asking "How do I limit the background processes of the apps?" You have two options:
1) Go to Network & Wireless>>Data Usage>>Restrict background data This will restrict apps running and using your data when you are using data only.
2) Go to Privacy>>Background apps>>Instagram you can un-check ...
No, there does not seem to be a way. However, I noticed the recent builds of Windows 10 Mobile are gradually starting to support or match the newer emojis.
Some emojis that were showing as boxes are now being correctly interpreted by apps like WhatsApp and Instagram, so, maybe the solution here is to just wait for the upcoming builds and hope they come ...