Introduction:

A typical cartoonish cactus usually looks like this:

enter image description here

One big stem in the middle, with some L-shaped branches sticking out.

We'll use this general shape for this challenge.

Challenge:

Given a pair of words, create an ASCII-art cactus with two upside down alphabets as stem. The first word is the left branch and the second word is the right branch:

E.g. input = ["cartoonish","testing"], will result in the following cactus:

 zz
 yy
 xx g
 ww n
 vv i
 uu t
 ttes
 ss
 rr
 qq
 pp
 oo
 nn
 mm
 ll
 kk
h jj
s ii
i hh
n gg
o ff
o ee
t dd
racc
 bb
 aa

The first letter of the words are part of the stem; then it'll grow out two letters; and continue upwards for the remaining letters.

Challenge rules:

• The words will have a guaranteed length of \5ドル \leq L \leq 99\$
• The words can start with an a or z, even though the resulting cactus might look pretty ridiculous that way; they can also start with the same letter or even be the same.
• A word can tower above the stem (e.g. yoghurt).
• Although leading spaces to have the correct shape are of course mandatory, one or more (additional) leading/trailing spaces or newlines are allowed. As long as the correct cactus is somewhere on the screen, it's fine.
• All the letters may be uppercase instead of lowercase, as long as its consistent across the entire 'cactus'.
• Output format is flexible, so can be printed to STDOUT; returned as a string; returned as a character-matrix; etc.

General Rules:

• This is code-golf, so the shortest answer in bytes wins.
  Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
• Standard rules apply for your answer with default I/O rules, so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters and return-type, full programs. Your call.
• Default Loopholes are forbidden.
• If possible, please add a link with a test for your code (e.g. TIO or ATO).
• Also, adding an explanation for your answer is highly recommended.

Test Cases:

Input: ["cartoonish","testing"]
Output:

 zz
 yy
 xx g
 ww n
 vv i
 uu t
 ttes
 ss
 rr
 qq
 pp
 oo
 nn
 mm
 ll
 kk
h jj
s ii
i hh
n gg
o ff
o ee
t dd
racc
 bb
 aa

Input: ["yoghurt","antidisestablishmentarianism"]
Output:

t
r
u
h zz m
goyy s
 xx i
 ww n
 vv a
 uu i
 tt r
 ss a
 rr t
 qq n
 pp e
 oo m
 nn h
 mm s
 ll i
 kk l
 jj b
 ii a
 hh t
 gg s
 ff e
 ee s
 dd i
 cc d
 bb i
 aant

Input: ["cactus","stems"]
Output:

 zz
 yy
 xx
 ww
 vv
 uu s
 tt m
 sste
 rr
 qq
 pp
 oo
 nn
 mm
 ll
 kk
 jj
 ii
 hh
 gg
s ff
u ee
t dd
cacc
 bb
 aa

Input: ["duplicate","duplicate"]
Output:

 zz
 yy
 xx
 ww
 vv
 uu
 tt
 ss
 rr
 qq
 pp
 oo
 nn
 mm
 ll
 kk
e jj e
t ii t
a hh a
c gg c
i ff i
l ee l
puddup
 cc
 bb
 aa