This is kind of awkward because of the way it is worded: neither ability says that you “double your Str bonus to damage” or similar, the verb is add not multiply. Strictly speaking, this does not trigger the usual multiplication rules, because the bonuses are separate things.
Moreover, at least from the quoted section, Master Samurai doesn’t seem to say that this addition is in replacement of the usual 1½ Str to damage. This implies an order of operations something like this:
Basic bastard sword damage when wielded in two hands:
Replace the 1½Str with 2Str due to Uncanny Blow:
Add 2Str due to Blades of Death:
1d10+2Str+2Str = 1d10+4Str
More than likely, however, the idea in both cases was of replacement and multiplying the same Strength bonus to damage, triggering the multiplication rules as SevenSidedDie suggests
Basic Strength bonus damage is replaced by Strength modifier doubled twice, which in the usual D&D rules is ×3, like so:
1½Str -> (1+(2-1)+(2-1)Str = 3Str
In any event, one or the other of these is certainly how the combination is supposed to work, and there’s nothing to suggest they shouldn’t be combined. So just ask your DM which calculation he wants to use. Personally, since I see all of the classes involved here as extremely underpowered, I probably wouldn’t object to the ×4, but the ×3 is probably the more reasonable interpretation of the intent if not the wording.
Note that in order to use both, though, you will need to treat the bastard sword as a one-handed exotic weapon, which you can only do with the Exotic Weapon Proficiency feat (or taking the nonproficiency penalty). This isn’s a big deal since Exotic Weapon Master requires that you have the feat in any event. You are never required to treat a bastard sword as a two-handed martial weapon; it’s just an option for getting around the nonproficiency penalty if you want. You may treat it as an exotic one-handed weapon any time you choose to, even if you choose to do so while using two hands.