They will normalize at 9-11 amps but I think when it is cold at first pull they will draw way more. IIRC someone was saying that they will pull around 60 each and then it comes down really fast, less than 1/2 second to the 9-11 amp area.
I am running all four on the 88 off of a single 40A automotive 4 blade relay. It still started with no issues last winter. The relay was used when I put it in, and is still fine. I have it setup with power directly from battery, relay, plugs. So like 13" tops.
I see no issue with your plan. It would be easier to use a single relay but if it's a matter of using what you have then go for it.
I need to get the glow plugs hooked up my Passat. I'm wondering best option. Id like to do it with the key but that may be more trouble than its worth? Sorry to hijack giz just didn't want to start another thread for it.