mt_product           | mt_sku                              | mt_price
==========           | ======                              | ========
id | brand_id | mpn  | id | product_id | retailer_id | sku | id | sku_id | price | date

SELECT
p.id AS pid, p.title AS p_title, p.cat, p.mpn,
b.id AS bid, b.name AS brand,
(SELECT COUNT(s.id) FROM mt_sku AS s WHERE s.pid = p.id) AS num_sku,
(SELECT COUNT(gbp.id) FROM mt_price AS gbp INNER JOIN mt_sku ON mt_sku.id = gbp.sid ) AS num_price
FROM mt_product AS p
INNER JOIN mt_brand b ON p.bid = b.id
INNER JOIN mt_sku s ON p.id = s.pid

SELECT
DISTINCT(p.id) AS pid, p.title AS p_title, p.cat, p.mpn,
b.id AS bid, b.name AS brand,
(SELECT COUNT(s.id) FROM mt_sku AS s WHERE s.pid = p.id) AS num_sku,
(SELECT COUNT(gbp.id) FROM mt_price AS gbp WHERE s.id = gbp.sid) AS num_price
FROM mt_product AS p
INNER JOIN mt_brand b ON p.bid = b.id
INNER JOIN mt_sku s ON p.id = s.pid