Suppose we start by evalutating the two sums in turn, where the
parameter $k\ge 1$.
For the first we will be using the following integral representation:
$${n+k\choose k}
= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{n+k}}{z^{k+1}} \; dz.$$
We seek $$\sum_{n\ge 1} {n-1+k\choose k} {n+k\choose k} x^n.$$
Using the integral we find
$$\frac{1}{2\pi i}
\int_{|z|=\epsilon}
\sum_{n\ge 1} {n-1+k\choose k} x^n
\frac{(1+z)^{n+k}}{z^{k+1}} \; dz
\\ = \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^k}{z^{k+1}}
\sum_{n\ge 1} {n-1+k\choose k} (1+z)^n x^n \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{x(1+z)^{k+1}}{z^{k+1}}
\sum_{n\ge 1} {n-1+k\choose k} (1+z)^{n-1} x^{n-1} \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{x(1+z)^{k+1}}{z^{k+1}}
\frac{1}{(1-x(1+z))^{k+1}} \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{x(1+z)^{k+1}}{z^{k+1}}
\frac{1}{(1-x-xz))^{k+1}} \; dz
\\= \frac{1}{(1-x)^{k+1}} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{x(1+z)^{k+1}}{z^{k+1}}
\frac{1}{(1-xz/(1-x)))^{k+1}} \; dz
\\ = \frac{x}{(1-x)^{k+1}}
\sum_{q=0}^k {k+1\choose k-q}
{q+k\choose k} \left( \frac{x}{1-x} \right)^q
\\ = \frac{x}{(1-x)^{k+1}}
\sum_{q=0}^k {k+1\choose q+1}
{q+k\choose k} \left( \frac{x}{1-x} \right)^q.$$
Applying the integral representation from the beginning a second time
we obtain for this sum
$$\frac{x}{(1-x)^{k+1}} \frac{1}{2\pi i}
\int_{|z|=\epsilon}
\sum_{q=0}^k {k+1\choose q+1}
\frac{(1+z)^{q+k}}{z^{k+1}}
\left( \frac{x}{1-x} \right)^q\; dz
\\ = \frac{x}{(1-x)^{k+1}} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^k}{z^{k+1}}
\sum_{q=0}^k {k+1\choose q+1}
(1+z)^q
\left( \frac{x}{1-x} \right)^q\; dz
\\ = \frac{1}{(1-x)^k} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
\sum_{q=0}^k {k+1\choose q+1}
(1+z)^{q+1}
\left( \frac{x}{1-x} \right)^{q+1}\; dz
\\ = \frac{1}{(1-x)^k} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
\left(-1 + \left(1+(1+z)\frac{x}{1-x}\right)^{k+1}\right) \; dz.$$
We have $k+1-(k-1) = 2$, so the first component inside the parentheses
drops out, leaving
$$ \frac{1}{(1-x)^k} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
\left(1+(1+z)\frac{x}{1-x}\right)^{k+1} \; dz
\\ = \frac{1}{(1-x)^{2k+1}} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
\left(1-x+x(1+z)\right)^{k+1} \; dz
\\ = \frac{1}{(1-x)^{2k+1}} \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
\left(1+xz\right)^{k+1} \; dz.$$
We need one more simplification on this and put $z=1/w$, getting
$$\frac{1}{(1-x)^{2k+1}} \frac{1}{2\pi i}
\int_{|w|=\epsilon} \frac{(1+1/w)^{k-1}}{(1/w)^{k+1}}
\left(1+x/w\right)^{k+1} \; \frac{1}{w^2} dw
\\ = \frac{1}{(1-x)^{2k+1}} \frac{1}{2\pi i}
\int_{|w|=\epsilon} w^2 (w+1)^{k-1}
\left(\frac{w+x}{w} \right)^{k+1} \; \frac{1}{w^2} dw
\\ = \frac{1}{(1-x)^{2k+1}} \frac{1}{2\pi i}
\int_{|w|=\epsilon} \frac{(w+1)^{k-1}}{w^{k+1}} (w+x)^{k+1}\; dw.$$
The reson this works is because we are essentially evaluating the residue at infinity and the residues sum to zero.
This concludes the evaluation of the first sum.
For the second we will be using the following integral representation:
$${k-1\choose j-1}
= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^j} \; dz.$$
We seek $$\sum_{j\ge 1} {k+1\choose j} {k-1\choose j-1} x^j.$$
Using the integral we find
$$\frac{1}{2\pi i}
\int_{|z|=\epsilon}
\sum_{j\ge 1} {k+1\choose j} x^j
\frac{(1+z)^{k-1}}{z^j} \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} (1+z)^{k-1}
\sum_{j\ge 1} {k+1\choose j} \frac{x^j}{z^j} \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} (1+z)^{k-1}
\left(-1 + (1+x/z)^{k+1} \right) \; dz.$$
The entire component drops out, leaving
$$\frac{1}{2\pi i}
\int_{|z|=\epsilon} (1+z)^{k-1}
(1+x/z)^{k+1} \; dz
\\= \frac{1}{2\pi i}
\int_{|z|=\epsilon} \frac{(1+z)^{k-1}}{z^{k+1}}
(z+x)^{k+1} \; dz.$$
This however is precisely the integral that we had for the first sum
without the factor in front, done.
The only infinite sum appearing here is the first one with convergence
when $|(1+z)x|<1.$ Therefore choosing $|x|\lt 1/Q$ and $|z|\lt 1/Q$
with $Q\ge 2$ we have $|(Q+1)/Q/Q|= |1/Q^2 + 1/Q|<1$ and get
convergence of the first LHS integral in a neighborhood of zero.
A trace as to when this method appeared on MSE and by whom starts at this
MSE link.