Prove or disprove $\sum\limits_{1\le i < j \le n} \frac{x_ix_j}{1-x_i-x_j} \le \frac18$ for $\sum\limits_{i=1}^n x_i = \frac12$($x_i\ge 0, \forall i$) 
Problem 1: Let $x_i \ge 0, \, i=1, 2, \cdots, n$ with $\sum_{i=1}^n x_i = \frac12$. Prove or disprove that
$$\sum_{1\le i < j \le n} \frac{x_ix_j}{1-x_i-x_j} \le \frac18.$$

This is related to the following problem:
Problem 2: Let $x_i \ge 0, \, i=1, 2, \cdots, n$ with $\sum_{i=1}^n x_i = \frac12$. Prove that
$$\sum_{1\le i<j\le n}\frac{x_ix_j}{(1-x_i)(1-x_j)}\le \frac{n(n-1)}{2(2n-1)^2}.$$
Problem 2 is in "Problems From the Book", 2008, Ch. 2, which was proposed by Vasile Cartoaje.
See: Prove that $\sum_{1\le i<j\le n}\frac{x_ix_j}{(1-x_i)(1-x_j)} \le \frac{n(n-1)}{2(2n-1)^2}$
Background:
I proposed Problem 1 when I tried to find my 2nd proof for Problem 2.
It is not difficult to prove that
$$\frac{1}{(2n-1)^4} + \frac{16n^2(n-1)^2}{(2n-1)^4}\cdot \frac{x_ix_j}{1-x_i-x_j}
\ge \frac{x_ix_j}{(1-x_i)(1-x_j)}.$$
(Hint: Use $\frac{x_ix_j}{(1-x_i)(1-x_j)}= 1 - \frac{1}{1 + x_ix_j/(1-x_i-x_j)}$
and $\frac{1}{1+u} \ge \frac{1}{1+v} - \frac{1}{(1+v)^2}(u-v)$
for $u = x_ix_j/(1-x_i-x_j)$ and $v=\frac{1}{4n(n-1)}$. Or simply
$\mathrm{LHS} - \mathrm{RHS} = \frac{(4x_ix_jn^2 - 4x_ix_j n + x_i + x_j - 1)^2}{(2n-1)^4(1-x_i-x_j)(1-x_i)(1-x_j)}\ge 0$.)
To prove Problem 2, it suffices to prove that
$$\frac{1}{(2n-1)^4}\cdot \frac{n(n-1)}{2} + \frac{16n^2(n-1)^2}{(2n-1)^4}\sum_{1\le i < j \le n} \frac{x_ix_j}{1-x_i-x_j} \le \frac{n(n-1)}{2(2n-1)^2} $$
or
$$\sum_{1\le i < j \le n} \frac{x_ix_j}{1-x_i-x_j} \le \frac18.$$
For $n=2, 3, 4$, the inequality is true.
For $n=5, 6$, numerical evidence supports the statement.
Any comments and solutions are welcome and appreciated.

Partial proof with hint :
Let us consider the inequality for $x,y>0$ and $x,y\leq 0.5$  :
$$l\left(x,y\right)=g\left(2xy+\frac{4}{3}xy\left(x-y\right)^{2}\right)-\frac{x^2y^2}{1-x^2-y^2}\ge 0$$
Where $g\left(x\right)=\frac{\frac{x^{2}}{4}}{1-x}$
As $g$ is convex on $[0,0.5]$ we use Jensen-Mercer inequality
We need to show :
$$\frac{n\left(n-1\right)}{2}\left(h\left(x,y\right)+h\left(a,b\right)-g\left(f\left(x,y\right)+f\left(a,b\right)-d\right)\right)\le\frac{1}{8}\tag{I}$$
Where $f\left(x,y\right)=2xy+\frac{4}{3}xy\left(x-y\right)^{2},h\left(x,y\right)=g\left(f\left(x,y\right)\right)$ and $f(a,b)\leq d \leq f\left(x,y\right)$
Now we use the inverse function of $f(x)$ with a positive value or :
$$r\left(x\right)=2\sqrt{x^{2}+x}-2x$$
So $(I)$ is true with the constraint (where we have used Karamata's inequality)
$$f\left(x,y\right)+f\left(a,b\right)\le r\left(\frac{\frac{1}{8}2}{n\left(n-1\right)}+g\left(f\left(x,y\right)+f\left(a,b\right)-d\right)\right)+r(0)$$
