first marathon and century 2 months before first HIM

I'm not sure what you mean by speedwork but if you mean going to a track and running intervals, then you don't need speedwork.  For a HIM, your limiter will not be your speed but your endurance.  I would follow the HIM plan of your choice which I'm guessing would not have any speedwork at all.  It may have you do one tempo run a week or may include pickups during one of runs but not going to the track to run intervals.

I'm also not sure of your goal for the HIM and the marathon but running the both so close together is going to impact both.  If the marathon is your A race and the HIM a C, then no problem but if the HIM is your A, then your not going to be at your best for the race.  It will take a couple of weeks to recover from a raced marathon and limit your ability to train.

I don't think the bike will be effected much by the marathon except for limiting available bike training time while you train for the marathon.  Of course, this is all contigent on your goals but since your question is about speed work, I'm guessing you want to race the HIM. 

Ernie

You don't need speedwork for your HIM.  You need endurance.

And your first marathon 2 months before your first HIM is generally not a good idea.

The problem, as Ernie mentioned, is that your taper & recovery from the marathon are going to severely limit your tri training during a period when you should be building up to you maximum load.  It can be done, but the HIM won't be your best.  And as each of these is your first at the distance, you may want to reconsider your plans.

I think a response is also dependent on your base fitness.  Are you only one or two years into this?

 If so you may be setting yourself up for some difficulty.  If you've been training consistently for several years it may not be that big of a deal.

Given that you are just doing your first mary and first century it may be wise to drop one of those, preferably your mary as they are harder to recover from than a century.

Recovery from the century should be no problem. If your marathon plan is the typical relatively low mileage beginner type of plan, your recovery time could potentially be significant. You may find it very difficult to do much run training for a month after the marathon and by that time you would be getting close to taper time for the HIM. Certainly you can do all 3 events, but be aware the HIM could turn into a sufferfest.

As others mentioned, there is no real speedwork necessary for a first time HIM. Your limiter will be endurance and the way to gain that is to ramp up the volume as much as is realistically possible, but not too fast or you could risk injury. If you were consistently running in excess of 45-50 miles/week for several months leading up to these races you would likely have little difficulty. However, as you would have needed to already be at that volume and your logs indicate you are nowhere close, your plan to do all 3 events fairly close together may not result in solid performances. No doubt you could finish all of them, but it sounds like your goals are more than just finishing. Whether just finishing is what you really want is something only you can decide.