The Japanese wiki has the HP values for all normal VRs, but bosses' HP in Force varies with the opponent and I tried to study it myself. Unfortunately I wasn't able to find enough patterns so I gave up on finishing. Before we start, little Jaguarandi has 1300 fixed HP like a normal VR. Target Ball (the tutorial's mini-Tangram) has 2000 HP but I didn't test if it changes with different opponents (which is not normally possible).
The bosses are Ajim, Guerlain, and big Jaguarandi. Ajim and Guerlain are always identical in HP to each other, and when fused into the single crystal all damage taken is halved, then doubled. Without going into details, my tests were precise enough to determine that the TRW of Temjin 747A does 224 damage against the crystal instead of 225 like normal. That won't affect much, but it matters for attacks that surpass the global 500 damage cap, like Raiden's turbo lasers. When separated, Ajim and Guerlain have super armor and take 10% damage from attacks, similar to Tangram and Z-Gradt in the previous games. In Arcade Mode on Easy their HP is reduced to 75% of normal, and on Very Easy their HP is reduced to 50% of normal. Harder difficulties do not increase HP. I didn't test if their HP is lowered with a continue.
Similarly for Jaguarandi, in Arcade Mode his HP is reduced to 75% on Easy, and 50% on Very Easy. Harder difficulties do not increase his HP. Note that in 1st and 2nd Operation of Mission Mode his AI is dumber but his HP has the normal value. Continuing lowers his HP like in all games, but I didn't test by how much. Big Jaguarandi's HP uniquely counts as 200% on the lifebar, which matters for timeouts. If he has a partner the lifebar can read 300% or 400%.
The HP for Ajim, Guerlain, and Jaguarandi varies according to both opponent VRs, so a huge table is needed to display all the possibilities. The order of the VRs matters, namely which one is the leader. Seat position does not matter. One hard pattern I found is that if you know the HP for a given ordering of two different VRs, and you also know the HP when either one of those VRs fights with an identical friend, there is a "mirror" formula to get the HP for the reverse order of the two different VRs. If one ordering is exceptionally favorable, the other ordering is always equally terrible.
There are soft patterns regarding some VR sub-models. For example if you know the HP when all sub-models of Fei-Yen pair with Temjin 747A, and when one Fei-Yen pairs with Guarayakha, you can extrapolate what happens when the other Fei-Yens pair with Guarayakha. So all the Fei-Yens are "grouped" together, however it is unconfirmed if the Fei-Yens stay grouped when pairings with all other VRs are considered. The groups don't strictly coincide with the base-models. Angelan "Love" and "Heal" appear to be in the same group but Angelan "Calm" is in its own group. I might not be looking at this in the best way; there might be better patterns to uncover.
Jaguarandi
Fei-Yen VH (x2): 3900
Fei-Yen BH (x2): 4100
Fei-Yen PH (x2): 4000
Fei-Yen CH (x2): 3900
Guarayakha (x2): 3250
Temjin 747A (x2): 6450
Temjin 747T (x2): 5375
Temjin 707J (x2): 6600
Angelan L (x2): 3400
Angelan H (x2): 2800
Angelan C (x2): 4075
Guerlain (x2): 5300
Fei-Yen VH (x1): 5100
Temjin 747A (x1): 5800
VH plus CH: 3900
CH plus VH: 3900
BH plus VH: 4100
VH plus BH: 3900
BH plus CH: 4100
CH plus BH: 3900
PH plus VH: 4000
PH plus BH: 4000
PH plus CH: 4000
VH plus PH: 3900
BH plus PH: 4100
CH plus PH: 3900
Guarayakha plus VH: 3700
Guarayakha plus BH: 3700
Guarayakha plus PH: 3700
Guarayakha plus CH: 3700
VH plus Guarayakha: 3450
BH plus Guarayakha: 3650
PH plus Guarayakha: 3550
CH plus Guarayakha: 3450
747A plus 747T: 5375
747T plus 747A: 6450
747A plus 707J: 6600
707J plus 747A: 6450
747T plus 707J: 6600
707J plus 747T: 5375
747A plus VH: 4600
747A plus BH: 4600
747A plus PH: 4600
747A plus CH: 4600
VH plus 747A: 5750
BH plus 747A: 5950
PH plus 747A: 5850
CH plus 747A: 5750
747A plus Guarayakha: 4150
Guarayakha plus 747A: 5550
Angelan L plus H: 3400
Angelan L plus C: 4475
Angelan H plus L: 2800
Angelan H plus C: 3875
Angelan C plus L: 3000
Angelan C plus H: 3000
L plus VH: 3700
L plus BH: 3700
L plus PH: 3700
L plus CH: 3700
H plus VH: 3100
H plus BH: 3100
H plus PH: 3100
H plus CH: 3100
C plus VH: 3300
C plus BH: 3300
C plus PH: 3300
C plus CH: 3300
VH plus L: 3600
BH plus L: 3800
PH plus L: 3700
CH plus L: 3600
VH plus H: 3600
BH plus H: 3800
PH plus H: 3700
CH plus H: 3600
VH plus C: 4675
BH plus C: 4875
PH plus C: 4775
CH plus C: 4675
Ajim or Guerlain
Fei-Yen VH (x2): 1925
Fei-Yen BH (x2): 1875
Fei-Yen PH (x2): 1900
Fei-Yen CH (x2): 1825
Guarayakha (x2): 1775
Temjin 747A (x2): 1875
Temjin 747T (x2): 2250
Temjin 707J (x2): 1925
Angelan L (x2): 1650
Angelan H (x2): 1175
Angelan C (x2): 1700
Guerlain (x2): 2250
Fei-Yen VH (x1): 3000
Temjin 747A (x1): 3000
VH plus CH: 1825
CH plus VH: 1925
BH plus VH: 1975
VH plus BH: 1825
BH plus CH: 1875
CH plus BH: 1825
PH plus VH: 2000
PH plus BH: 1900
PH plus CH: 1900
VH plus PH: 1825
BH plus PH: 1875
CH plus PH: 1825
Guarayakha plus VH: 1925
Guarayakha plus BH: 1825
Guarayakha plus PH: 1825
Guarayakha plus CH: 1825
VH plus Guarayakha: 1775
BH plus Guarayakha: 1825
PH plus Guarayakha: 1850
CH plus Guarayakha: 1775
747A plus 747T: 2125
747T plus 747A: 2000
747A plus 707J: 1875
707J plus 747A: 1925
747T plus 707J: 2000
707J plus 747T: 2175
747A plus VH: 1925
747A plus BH: 1825
747A plus PH: 1825
747A plus CH: 1825
VH plus 747A: 1875
BH plus 747A: 1925
PH plus 747A: 1950
CH plus 747A: 1875
747A plus Guarayakha: 1775
Guarayakha plus 747A: 1875
Angelan L plus H: 1725
Angelan L plus C: 1675
Angelan H plus L: 1100
Angelan H plus C: 1125
Angelan C plus L: 1675
Angelan C plus H: 1750
L plus VH: 1825
L plus BH: 1725
L plus PH: 1725
L plus CH: 1725
H plus VH: 1275
H plus BH: 1175
H plus PH: 1175
H plus CH: 1175
C plus VH: 1850
C plus BH: 1750
C plus PH: 1750
C plus CH: 1750
VH plus L: 1750
BH plus L: 1800
PH plus L: 1825
CH plus L: 1750
VH plus H: 1825
BH plus H: 1875
PH plus H: 1900
CH plus H: 1825
VH plus C: 1775
BH plus C: 1825
PH plus C: 1850
CH plus C: 1775
In certain Arcade Operation Missions it is possible to fight the bosses with just a single VR and no friend. The HP values in those battles are unusual and unfortunately seem to have no pattern or relation to the normal HP values.