delphi - What design pattern should I choose for different classes with common ancestor and common descendants? -

i'm refactoring of code @ moment. got 2 - redundant - units, 1 each product. both contain baseclass inherits few subclasses. these inherit more subclasses, well.

now want merge both units, redundant code won't redundant anymore , differing parts implemented separately in 2 different units.

i first thought of hierarchie following:

                        baseclass                            / \                           /   \                          /     \                         /       \                        /         \                       /           \                      /             \                     /               \                    /                 \                   /                   \          product<a>baseclass   product<b>baseclass                   \                   /                    \                 /                     \               /                      \             /                       \           /                        \         /                         \       /                          \     /                           \   /                            \ /                             x                            /|\                           / | \                          /  |  \                         /   |   \                        /    |    \                       /     |     \                      /      |      \                     /       |       \                    /        |        \                   /         |         \                  /          |          \                 /           |           \                /            |            \          subclass<1>   subclass<2>   subclass<3>              / \                          |             /   \                         |            /     \                        |           /       \                       |          /         \                      |         /           \                     |        /             \                    | subclass<1.1>   subclass<1.2>       subclass<3.1> 

but problem x, inheritance joins underneath product-specific classes, such inheritance isn't possible in delphi language.

so, think there has design pattern, useful implement such model common parent class , common descendant classes?

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edit: made uml class diagram clarify current situation.

without seeing actual classes nor knowing trying achieve difficult give answer, because there many considerations.

true multiple inheritance of c++ not possible. can similar interfaces not seem appropriate here because have not indicated classes derive solely or b, if implemented them have move actual function definitions x anyway.

but x? consider logically. if is, say, fruit , b round , x orange, ngln says need merge , b x, (or baseclass) , throw , b away.

on other hand if were, petrol tank, b headlight , x car, x contain 2 class members , b, , subclasses reference members.

on third hand if there classes derived solely , solely b may choose use interfaces , live fact implementations may have duplicated in descendants of (and separately in b) , in x, or, perhaps equivalently, derive x baseclass , duplicate functions of b , c in x. neither of these last 2 options ideal, , may choose merge them anyway , derive x regardless of if or b.