First things first... Have you checked to make sure the TV's sound works okay with a normal aerial or DVD feed? Second; most of the basic video senders have a selection switch for two or three different frequencies. Check the rear panel on each device. It may be that changing the frequency helps move the signal away from whatever the source of the interference is.
Products such as that Digisender are the cheap and cheerful solution to distributing TV around the house. The tick the average Joe's boxes....
1) simple to install
2) allows remote control of the source box
3) doesn't cost much
There's a step-up range of products along the same lines: Still wireless, but use a higher frequency (5GHz as opposed to 2.4GHz). This means they have a little more immunity to wireless interference.
The thing is though that these are still just a medium term solution. Wireless is used by a lot of equipment. The 5Ghz wireless is now pretty standard for a lot of product. So the crowding problems that forced the change from 2.4 to 5 will also affect 5Ghz sometime in the not too distant future. However, unless you're prepared to run cable then a wireless sender - even a 5Ghz one - is still going to be the cheapest/easiest solution.
If you're happy to run TV coax to the two other sets then there's a clever little box called a Tri-Link
http://www.satcure.co.uk/tech/trilink.htm that hooks up to the SCART socket on the TiVo and then sends picture and sound to the other TVs. It also does the remote relay thing. That's done by adding some Sky Eyes. These are little infra-red receivers for each remote TV location. They have a plug and socket arrangment so they connect inline with the aerial cable to each TV. That's how the IR signals get back to the TiVo box; back down the aerial cable.
Before going any further you do need to check that the two remote TVs have an analogue tuner each. i.e. they could pick up the old BBC1/BBC2/ITV/Ch4 etc before the move to digital. The simple way to do this is from the tuning menu. If you have options for both digital and analogue then you're set.
The Tri-link kit plus a suitable splitter/amplifier to distribute to more than 1 TV and a couple of Sky Eyes will set you back about £100. The cost might be lower if you have a suitable existing TV aerial splitter/amp.
Beyond this the costs rise considerably, but so does the quality. It is possible to distribute HD quality to all the TVs.