Assume (2) holds. Then $I$ is contained in the Jacobson radical of $A$, since otherwise there would be a nonunit $f \in A$ congruent to $1$ modulo $I$ and the map $A \to A_f$ would contradict (2). Hence $IB \subset B$ is contained in the Jacobson radical of $B$ for $B$ integral over $A$ because $\Spec(B) \to \Spec(A)$ is closed by Algebra, Lemmas \ref{algebra-lemma-going-up-closed} and \ref{algebra-lemma-integral-going-up}. Thus the map from idempotents of $B$ to idempotents of $B/IB$ is injective by Lemma \ref{lemma-idempotents-determined-modulo-radical}. On the other hand, since (2) holds, every idempotent of $B/IB$ lifts to an idempotent of $B$ by Lemma \ref{lemma-lift-idempotent-upstairs}. In this way we see that (2) implies (4). \medskip\noindent The implication (4) $\Rightarrow$ (3) is trivial. \medskip\noindent Assume (3). Let $\mathfrak m$ be a maximal ideal and consider the finite map $A \to B = A/(I \cap \mathfrak m)$. The condition that $B \to B/IB$ induces a bijection on idempotents implies that $I \subset \mathfrak m$ (if not, then $B = A/I \times A/\mathfrak m$ and $B/IB = A/I$). Thus we see that $I$ is contained in the Jacobson radical of $A$. Let $f \in A[T]$ be monic and suppose given a factorization $\overline{f} = g_0h_0$ with $g_0, h_0 \in A/I[T]$ monic. Set $B = A[T]/(f)$. Let $\overline{e}$ be the idempotent of $B/IB$ corresponding to the decomposition $$ B/IB = A/I[T]/(g_0) \times A[T]/(h_0) $$ of $A$-algebras. Let $e \in B$ be an idempotent lifting $\overline{e}$ which exists as we assumed (3). This gives a product decomposition $$ B = eB \times (1 - e)B $$ Note that $B$ is free of rank $\deg(f)$ as an $A$-module. Hence $eB$ and $(1 - e)B$ are finite locally free $A$-modules. However, since $eB$ and $(1 - e)B$ have constant rank $\deg(g_0)$ and $\deg(h_0)$ over $A/I$ we find that the same is true over $\Spec(A)$. We conclude that \begin{align*} f & = \text{CharPol}_A(T : B \to B) \\ & = \text{CharPol}_A(T : eB \to eB) \text{CharPol}_A(T : (1 - e)B \to (1 - e)B) \end{align*} is a factorization into monic polynomials reducing to the given factorization modulo $I$. Here $\text{CharPol}_A$ denotes the characteristic polynomial of an endomorphism of a finite locally free module over $A$. If the module is free the $\text{CharPol}_A$ is defined as the characteristic polynomial of the corresponding matrix and in general one uses Algebra, Lemma \ref{algebra-lemma-standard-covering} to glue. Details omitted. Thus (3) implies (1). \medskip\noindent Assume (1). Let $f$ be as in (5). The factorization of $f \bmod I$ as $T^n$ times $T - 1$ lifts to a factorization $f = gh$ with $g$ and $h$ monic by Definition \ref{definition-henselian-pair}. Then $h$ has to have degree $1$ and we see that $f$ has a root reducing to $1$ modulo $1$. Finally, $I$ is contained in the Jacobson radical by the definition of a henselian pair. Thus (1) implies (5). \medskip\noindent Before we give the proof of the last step, let us show that the root $\alpha$ in (5), if it exists, is unique. Namely, Due to the explicit shape of $f(T)$, we have $f'(\alpha) \in 1 + I$ where $f'$ is the derivative of $f$ with respect to $T$. An elementary argument shows that $$ f(T) = f(\alpha + T - \alpha) = f(\alpha) + f'(\alpha) \cdot (T - \alpha) \bmod (T - \alpha)^2 A[T] $$ This shows that any other root $\alpha' \in 1 + I$ of $f(T)$ satisfies $0 = f(\alpha') - f(\alpha) = (\alpha' - \alpha)(1 + i)$ for some $i \in I$, so that, since $1 + i$ is a unit in $A$, we have $\alpha = \alpha'$. \medskip\noindent Assume (5). We will show that (2) holds, in other words, that for every \'etale map $A \to A'$, every section $\sigma : A' \to A/I$ modulo $I$ lifts to a section $A' \to A$. Since $A \to A'$ is \'etale, the section $\sigma$ determines a decomposition \begin{equation} \label{equation-GCHP} A'/IA' \cong A/I \times C \end{equation} of $A/I$-algebras. Namely, the surjective ring map $A'/IA' \to A/I$ is \'etale by Algebra, Lemma \ref{algebra-lemma-map-between-etale} and then we get the desired idempotent by Algebra, Lemma \ref{algebra-lemma-surjective-flat-finitely-presented}. We will show that this decomposition lifts to a decomposition  \begin{equation} \label{equation-GCHP-want} A' \cong A'_1 \times A'_2 \end{equation} of $A$-algebras with $A'_1$ integral over $A$. Then $A \to A'_1$ is integral and \'etale and $A/I \to A'_1/IA'_1$ is an isomorphism, thus $A \to A'_1$ is an isomorphism by Lemma \ref{lemma-check-isomorphism-zariski} (here we also use that an \'etale ring map is flat and of finite presentation, see Algebra, Lemma \ref{algebra-lemma-etale}). \medskip\noindent Let $B'$ be the integral closure of $A$ in $A'$. By Lemma \ref{lemma-helper-finite-type} we may decompose  \begin{equation} \label{equation-dec-mod-I} B'/IB' \cong A/I \times C' \end{equation} as $A/I$-algebras compatibly with (\ref{equation-GCHP}) and we may find $b \in B'$ that lifts $(1, 0)$ such that $B'_b \to A'_b$ is an isomorphism. If the decomposition (\ref{equation-dec-mod-I}) lifts to a decomposition \begin{equation} \label{equation-want-2} B' \cong B'_1 \times B'_2 \end{equation} of $A$-algebras, then the induced decomposition $A' = A'_1 \times A'_2$ will give the desired (\ref{equation-GCHP-want}): indeed, since $b$ is a unit in $B'_1$ (details omitted), we will have $B'_1 \cong A'_1$, so that $A'_1$ will be integral over $A$.  \medskip\noindent Choose a finite $A$-subalgebra $B'' \subset B'$ containing $b$ (observe that any finitely generated $A$-subalgebra of $B'$ is finite over $A$). After enlarging $B''$ we may assume $b$ maps to an idempotent in $B''/IB''$ producing \begin{equation} \label{equation-again-dec-mod-I} B''/IB'' \cong C''_1 \times C''_2 \end{equation} Since $B'_b \cong A'_b$ we see that $B'_b$ is of finite type over $A$. Say $B'_b$ is generated by $b_1/b^n, \ldots, b_t/b^n$ over $A$ and enlarge $B''$ so that $b_1, \ldots, b_t \in B''$. Then $B''_b \to B'_b$ is surjective as well as injective, hence an isomorphism. In particular, we see that $C''_1 = A/I$! Therefore $A/I \to C''_1$ is an isomorphism, in particular surjective. By Lemma \ref{lemma-helper-finite} we can find an $f(T) \in A[T]$ of the form $$ f(T) = T^n(T - 1) + a_n T^n + \ldots + a_1 T + a_0 $$ with $a_n, \ldots, a_0 \in I$ and $n \ge 1$ such that $f(b) = 0$. In particular, we find that $B'$ is a $A[T]/(f)$-algebra. By (5) we deduce there is a root $a \in 1 + I$ of $f$. This produces a product decomposition $A[T]/(f) = A[T]/(T - a) \times D$ compatible with the splitting (\ref{equation-dec-mod-I}) of $B'/IB'$. The induced splitting of $B'$ is then a desired (\ref{equation-want-2}).