Internal Knowledge Base Chat Tool

I want to build an internal knowledge base tool for my legal team. We have 4 years of case notes, contracts, and internal memos (600 documents across Google Drive and Dropbox). It takes forever to find anything. I need someone to train a language model using these documents and create a simple chat tool where my team can ask questions. The tool should also be hosted in a secure environment. As a deliverable, I expect a working internal tool with basic access controls and documentation for our IT team to maintain it.