Alright, let me answer this from a lore and logic point of view, as well as taking realistic circumstances into account.
As already mentioned by ironboundtome, Space Marine weapons are already larger than those of reuglar humans to make up for their size, this means that a Space Marine chainsword is probably too heavy to be used by any kind of human in one hand, and probably not even with two hands unless he is the new hulk of the imperium.
Now, by means of Strength it should be no problem for a space marine to simply carry two large weapons, however, it should be a problem to use them continiously. If we look at the animations of Space Marines in like, let's say the Space Marine video game (not saying its a good source of perfectly researched lore and such, just taking it as an example) then you can clearly see that when wielding two handed weapons they don't fling them arround like little toys.
Even if Strength wouldn't be a problem- have you ever tried to use two two-handed wooden swords as a kid? Fighting with two weapons is a hard enough task as it is- now taking into consideration how LONG those are in this example it gets really hard. Once you get swing into a heavy object it logically takes time to stop it, or change its direction, this gets even worse the longer the weapon gets which is why they usually have a larger handle to use both hands at once in order to be able to use the 2nd hand to direct the weapon and movements of it.
However, I think it depends on the weapon, and how the character intends to use it. I for myself would probably allow it, but make it harder to use both weapons as it is obviously a more difficult task than simply attacking with two normal sized weapons.