Okay I am just going to give basic information so that you and your son can have a good go with the models you currently have. If you find you like what you see I encourage picking up the main rule book and the corresponding indexes for your armies.Sorry this did not format well from my Word doc.
From the Battle of McCragge set you had ten man Space Marine tactical squad, ten Termagants, six Genestealers and eight spore mines. You have stated you have added to this over time but this is what I am going to go on. Plus I am not including all the special rules or points. However, I am providing the Power Rating for the forces which I think is a good way to play the new 8th edition rules.
Space Marine Tactical Squad: Power Rating is 5 that includes 4 marines and a sergeant, and increase of five more models raises the Power Rating to 9. All models come armed with a bolt gun, bolt pistol and frag and krack grenades.
Move: 6", Weapon Skill 3+, Ballistic Skill 3+, Strength 4, Toughness 4, Wounds 1, Attacks 1, Leadership 7, Save 3+
Marine sergeant has the same stat line except for having 2 attacks and a leadership of 8
Weapons Range Strength AP Damage
Bolt Pistol 12" 4 0 1 Pistol 1
Bolt gun 24" 4 0 1 Rapid Fire 1
Krack Grenade 6" 6 -1 D3 Grenade 1
Frag Grenade 6" 3 0 1 Grenade D6 hits
Flamer 8" 4 0 1 Assault D6 auto hits
MissileLauncher 48"
Frag Missile 4 0 1 Heavy D6
Krack Missile 8 -2 D6 Heavy 1
Space Marines can re-roll failed morale tests
Genestealers: Unit starts with five Genestealers for a power rating of 4 and can be increased up to ten models for a total power rating of 8 another.
Move: 8", Weapon Skill 3+, Ballistic Skill none, Strength 4, Toughness 4, Wounds 1, Attacks 3, Leadership 9, Save 5+ invulnerable
Weapons Range Strength AP Damage Notes
Rending claws Melee user -1 1 Each wound roll of 6+ is resolved as AP -4
Termagants: Unit contains 10 Termagants for a power rating of 3
Move: 6", Weapon Skill 4+, Ballistic Skill 4+, Strength 3, Toughness 3, Wounds 1, Attacks 1, Leadership 5, Save 6+
Weapons Range Strength AP Damage
Notes
Fleshborer 12" 4 0 1 Assault 1
Spore Mines: Unit contains 3 spore mines for a power rating of 1 and can be increased to six models for a total power rating of 2
Move: 3", Weapon Skill -, Ballistic Skill -, Strength 1, Toughness 1, Wounds 1, Attacks 1, Leadership 10, Save 7+
Float Down: During deployment you can set up a spore mine in the upper atmosphere instead of the battlefield. At the end of any of you Movement phases it can float down and set up anywhere that is more than 12' away from an enemy model.
Floating Death: spore mines explodes if it is within 3' of any enemy model at the end of the charge phase. Roll a D6 for each spore mine, on a 1 if fails to cause any damage on a 2-5 it inflicts one Mortal Wound, on a 6 it inflicts D3 Mortal Wounds. The Spore Mine is then destroyed.
Living Bombs: Spore Mines automatically pass morale tests and count as victory points to the opposing player for being destroyed .
