diff --git a/pyhgf/model/add_nodes.py b/pyhgf/model/add_nodes.py
index 4a40ab525..ea928cc05 100644
--- a/pyhgf/model/add_nodes.py
+++ b/pyhgf/model/add_nodes.py
@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from copy import deepcopy
-from typing import TYPE_CHECKING, Callable, Dict, List, Optional, Tuple
+from typing import TYPE_CHECKING, Callable, Dict, List, Optional, Tuple, Union
 
 import jax.numpy as jnp
 
@@ -27,7 +27,6 @@ def add_continuous_state(
     coupling_fn: Tuple[Optional[Callable], ...],
 ):
     """Add continuous state node(s) to a network."""
-
     node_type = 2
 
     default_parameters = {
@@ -80,7 +79,6 @@ def add_binary_state(
     additional_parameters: Dict,
 ):
     """Add binary state node(s) to a network."""
-
     # define the type of node that is created
     node_type = 1
 
@@ -119,10 +117,9 @@ def add_ef_state(
     n_nodes: int,
     node_parameters: Dict,
     additional_parameters: Dict,
-    value_children: Optional[Tuple[Optional[Tuple]]],
+    value_children: Tuple = (None, None),
 ):
     """Add exponential family state node(s) to a network."""
-
     node_type = 3
 
     default_parameters = {
@@ -174,7 +171,6 @@ def add_categorical_state(
     network: Network, n_nodes: int, node_parameters: Dict, additional_parameters: Dict
 ) -> Network:
     """Add categorical state node(s) to a network."""
-
     node_type = 5
 
     if "n_categories" in node_parameters:
@@ -233,7 +229,6 @@ def add_dp_state(
     network: Network, n_nodes: int, node_parameters: Dict, additional_parameters: Dict
 ):
     """Add a Dirichlet Process node to a network."""
-
     node_type = 4
 
     if "batch_size" in additional_parameters.keys():
@@ -273,13 +268,12 @@ def add_dp_state(
 
 
 def get_couplings(
-    value_parents: Optional[Tuple],
-    volatility_parents: Optional[Tuple],
-    value_children: Optional[Tuple],
-    volatility_children: Optional[Tuple],
+    value_parents: Optional[Union[Tuple, List, int]],
+    volatility_parents: Optional[Union[Tuple, List, int]],
+    value_children: Optional[Union[Tuple, List, int]],
+    volatility_children: Optional[Union[Tuple, List, int]],
 ) -> Tuple[Tuple, ...]:
     """Transform coupling parameter into tuple of indexes and strenghts."""
-
     couplings = []
     for indexes in [
         value_parents,
@@ -301,14 +295,13 @@ def get_couplings(
             coupling_idxs, coupling_strengths = None, None
         couplings.append((coupling_idxs, coupling_strengths))
 
-    return couplings
+    return tuple(couplings)
 
 
 def update_parameters(
     node_parameters: Dict, default_parameters: Dict, additional_parameters: Dict
 ) -> Dict:
-    """Update the default node parameters using keywords args and dictonary"""
-
+    """Update the default node parameters using keywords args and dictonary."""
     if bool(additional_parameters):
         # ensure that all passed values are valid keys
         invalid_keys = [
@@ -345,10 +338,9 @@ def insert_nodes(
     volatility_parents: Tuple = (None, None),
     value_children: Tuple = (None, None),
     volatility_children: Tuple = (None, None),
-    coupling_fn: Optional[Tuple[Optional[Callable], ...]] = (None,),
+    coupling_fn: Tuple[Optional[Callable], ...] = (None,),
 ) -> Network:
     """Insert a set of parametrised node in a network."""
-
     # ensure that the set of coupling functions match with the number of child nodes
     if value_children[0] is not None:
         if value_children[0] is None:
diff --git a/pyhgf/model/network.py b/pyhgf/model/network.py
index c6700cc8c..3eec09908 100644
--- a/pyhgf/model/network.py
+++ b/pyhgf/model/network.py
@@ -567,6 +567,3 @@ def add_edges(
         self.edges = edges
 
         return self
-
-
-# Functions to be added