If it's a private group (and not a channel) you can download them in bulk using the official telegram app.
Go to Settings -> advanced -> export telegram data (at the end). A pop-up window will appear that asks what data you want to export. Select only private groups and UNCHECK "only my messages" in order to download all chat history. Then you can select what data to download (photos, videos, voice messages, files, gifs...). Select the path where download the data and click export.
I've been using Terabox for 6 months now and it's still working. I uploaded many ISO files and lots of movies/tv series.
I don't suggest you to upload sensitive files and to accept the risk that they can suddenly remove all your data without advising you. They haven't done yet, but they could do that (also Google did that with unlimited storage).
If you want to upload videos or other stuff that isn't very important for you (like videos that you can re-download anytime) probably it is fine, but if you want to store important data I don't recommend it.