Yea you can bring it in house. Can you purchase the existing software? Then rather than do a rewrite, work towards rebuilding/refactoring. Please dont listen to the people here telling you to do a rewrite. It will fail or go way longer than you expect with many issues.
If you can start hiring some devs/UX/infra people and work alongside exiting team. Once they build up knowledge and are ready to take over the project, then they can start taking proper ownership and rebuilding and extending parts of the system. Slowly slowly you will not only build up the expertise and team but be will have a fully functioning dev team owning the system end to end. Focus on hiring good people with a strong focus on senior people and building up knowledge of the software system.