I've got a fair amount of experience with fighting IC's (my main practice partner is an IC beast), but I've just now started using Lucas (I'm a Toon Link main). What has been said is exceedingly important -- Don't. Get. Grabbed. That's really your first step, as the chain grab is just absolutely lethal.
To address ice block spam, I recommend getting used to quick shorthops with projectile counterattacks in between -- this is PK Fire for Lucas. If you time it right, and space yourself well, you can hop barely over the two blocks (or even three or more, depending on placement and if the IC player is desyncing them), and shoot off a pk fire in the air at a level barely over the height of a complete ice block. I've had some luck with this, as once I got the timing down I can shut down the spam, and move in for an aerial combo. Depending on your friend's playstyle, you really want to avoid running head on (or jumping, rather) into them when they're ice blocking -- they'll hit you with a blizzard. However, a good way to mindgame them out of this is to predict this happening, and space yourself with the magnet coming in -- you can absorb some of the blizzard, and if you've spaced perfectly, you can let go and hit them with the "pop" (or w/ever you call that). This can lead to combos or separation.
Separating the IC's can be a pain, and once they're separated, most people don't know what to do with them. You have to remember that Nana, while stupid (the comp control is really not intelligent) is not entirely out of the player's control -- It's possible, depending on how the desync happened, for the player to use Nana to grab you or dodge your attacks, even when Popo's accross the map. This is something you need to look out for, because at high enough percentages it can lead to a chain-grab smash (one holds, other charges). Your danger zone (where a single charged upsmash will almost certainly kill you) is about 80-90%. To take care of Nana when she's away, try hitting her with a PK Fire (if Popo won't punish), or a longer aerial (nair seems good). The player may be able to time the airdodge, but it'll be harder with a longer duration move... especially if you sync up with her so you fall next to her. Keeping them separated isn't a guaranteed win, but it'll make a lot of the strategies that they use not work. If Nana's off the stage, you can be a little more aggressive with Popo, not worrying about chain grabs. IC players have to keep track of two characters, and they can almost never perfect shield an AOE attack -- Nana's got a lag to when she shields and dodges, so they have to shield early. Take advantage of that too -- If you can, the d-smash is absolutely amazing. Try to manipulate them into going for a grab or rolling towards you, and pull it out. Even if Popo shields, Nana's almost certainly getting hit.
And of course, remember -- Nana's got a separate damage %... She'll often go flying further than Popo, so abuse this fact and go for Popo in the air.
As for other approaches, try short hopping the dair right above their heads, and short hopping nair at their backs (if you can, DI back the way you came, as it's harder to grab you if you're moving unpredictably).
Good luck!
PS: You may want to check out some of the matches with ICYDP in my Youtube account (linked in sig), that's the IC player I play against. None of them were great matches (we were all kinda screwing around the day we recorded), and I don't think there are any Lucas v IC matches up, but you can analyze different characters approaches and see what works/doesn't work. IC's are a tricky bunch to lay against, so just keep at it!
also u can use the side smash to reflect blizzard if timed right
