I am in this part of the game where you must use this spell to get the "Answers to Life and Death" part that takes place in Skae Brae complete, but there is one problem. According to Ultima Codex, you must have blood moss, mandrake root, nightshade, spider silk, and sulfurous ash, which I am very sure I bought those, and upon scrolling to the right page, the spell refuses to cast on the mayor when I double click on it on the appropriate page on the spellbook. Is something amiss? Did I need to level up characters, or was there something else I should have done aside from getting the spellbook, purchasing the spell, and the items required to cast it? Any help is greatly appreciated!

The ingredients are indeed correct. The only thing I can think of is that you're not level 4 yet.
Your character needs to be at least the same level as the spell you're trying to cast.
The first page has no circle and has free to cast spells, but every page after that requires a level.
The first circle requires level one, second circle requires level 2 and so on.

You don't need to target the seance spell by the way. When you're level 4, just cast it and you'll be able to talk to every ghost for a time.

What makes me wonder is how you got on the island though, since you need the spell to talk to the ferryman. Although there's an overlooked spot on the island where you can just squeeze in a magic carpet.

I did indeed squeeze in the magic carpet every time I went into the island. I know this may sound silly, but do I just simply fight enemies with or without magic until I level up to level 4? Thanks!

Killing enemies gives you XP, as will certain events (one at the very end of the game gives you a lot of XP that you probably won't use, for example). To reach level 4, you need to have at least 400 XP. If it's like previous Ultima games, only the character who kills the enemy is awarded XP, so you will need to have the Avatar get the XP you need, since she is the only one in the party who can cast spells.

I don't remember if talking to Lord British is necessary in U7 (I happen to not like this particular Ultima, so I don't remember it as well as the others), but I do remember that you get training points when you gain levels. You can boost your stats by finding a trainer and paying for training, provided you have enough training points. Note that each trainer gives you different stat boosts, so find the trainers that you want. (I note that INT and Magic are useful for the Avatar, but not useful for other characters.)

I want to thank both of you guys for the replies, and I'll make sure to go do that!

Since dtgreene mentioned trainers, there are a lot of them in Britannia and some are a lot more useful than others.
This might help:
https : //strategywiki.org/wiki/Ultima_VII:_The_Black_Gate/Trainers

Edit: Hmm, why is this forum making a mess of links? I put a couple of spaces around the : to fix it.

Completing Forge of Virtue will also max out your stats, with your strength rising up to double the max. It is almost cheating

Actually, there's a glitch that lets you get maxed stats without Forge of Virtue, with even more Strength. To do this, just take 6 ((IIRC) doses of Silver Serpent Venom all at once; when they wear off, you will have maxed stats and over 250 Strength. There, is, however, one drawback; the game will treat your maximum health as being negative, which could be a (rather serious) problem.

Taking one more does will fix your Strength, but when it wears off, your stats will go back down to 24.

For those who aren't aware, when you take a dose, your stats increase by 5; when they wear off; your stats decrease by 6, resulting in a net loss. You can, however, use this to your advantage by training Combat or Magic while under the effects; one training point will raise Combat or Magic by half the difference between it and your Dexterity/Intelligence.

Isn't this a lot more interesting than just completing Forge of Virtue?

(Disclaimer: Exult may behave differently here.)