Hello NiceMathophile welcome to M.S.E.
Here's a hint to solve the problem;
Can you show that $\sqrt{b-1}+\sqrt{c-1}\leq \sqrt{bc},$ and then show that $\sqrt{a-1}+\sqrt{bc}\leq \sqrt{a(bc+1)}$?
Use Cauchy Schwartz inequality in both cases.
If you are done solving the problem, you can take a look at the answer below (spoiler alert);
We know that this inequality is non-symmetric in general which makes it hard to try and solve, but it is symmetric in $b$ and $c$. So we will first find a bound on $\sqrt{b-1}+\sqrt{c-1},$ and then approach to solve the entire problem. By the Cauchy Schwartz inequality, we have;\begin{align*}\left(\sqrt{(b-1)\cdot 1}+\sqrt{1\cdot(c-1)}\right)^2 &\leq \left((b-1)+1\right)\left(1+(c-1)\right)\\ & \leq bc.\end{align*} Now, taking the Square Root gives us;\begin{align*}\sqrt{b-1}+\sqrt{c-1} &\leq \sqrt{bc}.\end{align*} Now, it suffices to show that;\begin{align*}\sqrt{a-1}+\sqrt{bc}\leq \sqrt{a(bc+1)}\end{align*} But by the Cauchy Schwartz inequality, we have;\begin{align*}&\left(\sqrt{(a-1)\cdot 1}+\sqrt{1\cdot bc}\right)^2\leq {\left((a-1)+1\right)(bc+1)}\\ \implies &\sqrt{a-1}+\sqrt{bc}\leq {a(bc+1)}.\end{align*}Thus, bringing it all together, we get that;$$\sqrt{a-1}+\sqrt{b-1}+\sqrt{c-1}\leq {a(bc+1)},$$ as required.