How do you manage if you find it hard to hire senior engineers to grow the engineering team?

You can split the engineering work into incremental vs drastic developments/changes. If you cannot afford to pay market rate salaries. You can bring in a solid consultant for architecture and design related aspects. Younger/hungry folks can be used for the execution and incremental changes. This way, you will be able to leverage their knowledge/inputs but at the same time be able to solve the specific problems you are facing in terms of engineering. Not a perfect way but this works if done patiently !!