First of all, you must realize that those additional UHF stations are in a COMPLETELY DIFFERENT Direction than your Locals...and Ch10 towards a THIRD Direction....so you'll have to use a ROTATOR....or a set of THREE Antennas, each pointed in a different direction. You COULD try a simple 2-Way RF Splitter/Combiner for the two UHF Antennas, but might have problems with the OMNI RCA Flat Panel injecting Man-Made Noise and Multipath into the weak signals on the OTHER Antenna(s)....a higher Gain, narrower Beamwidth Antenna could HELP this situtation. If this is a problem [check each Antenna individually first], you will need to use SEPARATE Coax Downleads and an RF A/B Switch (you can still get R-S Remote Controlled RF A/B Switch on FleaBay).
ANTOP UHF-262 Specs says it provides 15.5 dB (dBd or dBi NOT stipulated and probably peaks well above OUR UHF Band), Front/Back Ratio = 25 dB and covers 470-862 MHz, so it is NOT Optimized for the (470-698 MHz) North American UHF TV Band....and although NOT specifically designed for Hi-VHF Band, will PROBABLY also receive Very Strong Ch12 and Ch13:
Also offered under the Stellar Labs name, with SAME ambiguous Gain Spec:
UHF-262 appears to be a KLONE of the old Televes DAT-43 (aka Triboom-46 in UK Aerials Report), which per fol. Gain Chart (in dBd, so add 2.15 for dBi) has a Gain of about 9.0 dBi on 470 MHz (US Ch14
~ Euro Ch21), rising to about 12.7 dBi on 698 MHz (US Ch51
~ Euro Ch49), eventually maxing out at about 15.2 dBi on 752 MHz (Old US Ch60 ~ Euro Ch52). So I'm going to guesstimate that ANTOP Max Gain Spec is 15.5 dBi (and NOT dBd)...uselessly stipulated for a MUCH higher Frequency than our UHF Band:
HOWEVER, my inexpensive Antenna of Choice would be the fol. Eagle 2-Bay Bowtie [buy TWO, they're cheap], which appears LARGE enough to provide performance "similar" to DIY M2 with a Screen Reflector (about 10-13 dBi):
If you decide to Build-Your-Own, my H2 with Reflector Rods is OPTIMIZED for our UHF Band and has sufficient Hi-VHF Gain and Multipath Rejection to also pick up Ch12 and Ch13:
To receive Ch10, you are going to need a THIRD Antenna with significant Gain in the Hi-VHF Band pointed in a DIFFERENT DIRECTION....or a ROTATOR. You might want to consider whether that channel is worth the cost of adding the fol. Stellar Lab Hi-VHF 12-El Yagi, pointed towards 79-deg (re True North), using a VHF/UHF Combiner:
They also offer a lower Gain, lower Cost 9-El Yagi:
Whatever you try, be sure you can economically RETURN it.
The above is the bare-bones budget suggestion that is worth trying to receive those distance stations....and may or may NOT work....Attic Loss and Multipath is very difficult to predict, even from up close. BTW: for Attic use and NM's in the 20's, I would normally recommend a MUCH Higher Gain Antenna, such as DB-8e, CM4228HD (with HHH mod) or DIY FF4/FF6 [the latter three have significant Hi-VHF Gain but poor SWR]:
Of course, the DB-8e could initially be configured with panels pointed in different directions...or SAME if higher Gain is found to be needed...BUT bear in mind that the PCB Balun will significantly attenuate your Very Strong Ch12 and Ch13 [probably NOT a problem, but if it is, you COULD fix by replacing PCB Balun with conventional Transformer Balun].